third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp

/*
 * Copyright (C) 2013 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#include "core/layout/LayoutBlockFlow.h"

#include "core/editing/Editor.h"
#include "core/frame/FrameView.h"
#include "core/frame/LocalFrame.h"
#include "core/html/HTMLDialogElement.h"
#include "core/layout/HitTestLocation.h"
#include "core/layout/LayoutAnalyzer.h"
#include "core/layout/LayoutFlowThread.h"
#include "core/layout/LayoutInline.h"
#include "core/layout/LayoutMultiColumnFlowThread.h"
#include "core/layout/LayoutMultiColumnSpannerPlaceholder.h"
#include "core/layout/LayoutPagedFlowThread.h"
#include "core/layout/LayoutView.h"
#include "core/layout/TextAutosizer.h"
#include "core/layout/line/GlyphOverflow.h"
#include "core/layout/line/InlineIterator.h"
#include "core/layout/line/InlineTextBox.h"
#include "core/layout/line/LineWidth.h"
#include "core/layout/shapes/ShapeOutsideInfo.h"
#include "core/paint/BlockFlowPaintInvalidator.h"
#include "core/paint/PaintLayer.h"
#include "wtf/PtrUtil.h"
#include <memory>

namespace blink {

bool LayoutBlockFlow::s_canPropagateFloatIntoSibling = false;

struct SameSizeAsLayoutBlockFlow : public LayoutBlock {
  LineBoxList lineBoxes;
  void* pointers[2];
};

static_assert(sizeof(LayoutBlockFlow) == sizeof(SameSizeAsLayoutBlockFlow),
              "LayoutBlockFlow should stay small");

struct SameSizeAsMarginInfo {
  uint16_t bitfields;
  LayoutUnit margins[2];
};

static_assert(sizeof(LayoutBlockFlow::MarginValues) == sizeof(LayoutUnit[4]),
              "MarginValues should stay small");

// Caches all our current margin collapsing state.
class MarginInfo {
  // Collapsing flags for whether we can collapse our margins with our
  // children's margins.
  bool m_canCollapseWithChildren : 1;
  bool m_canCollapseMarginBeforeWithChildren : 1;
  bool m_canCollapseMarginAfterWithChildren : 1;
  bool m_canCollapseMarginAfterWithLastChild : 1;

  // Whether or not we are a quirky container, i.e., do we collapse away top and
  // bottom margins in our container. Table cells and the body are the common
  // examples. We also have a custom style property for Safari RSS to deal with
  // TypePad blog articles.
  bool m_quirkContainer : 1;

  // This flag tracks whether we are still looking at child margins that can all
  // collapse together at the beginning of a block. They may or may not collapse
  // with the top margin of the block (|m_canCollapseTopWithChildren| tells us
  // that), but they will always be collapsing with one another. This variable
  // can remain set to true through multiple iterations as long as we keep
  // encountering self-collapsing blocks.
  bool m_atBeforeSideOfBlock : 1;

  // This flag is set when we know we're examining bottom margins and we know
  // we're at the bottom of the block.
  bool m_atAfterSideOfBlock : 1;

  // These variables are used to detect quirky margins that we need to collapse
  // away (in table cells
  // and in the body element).
  bool m_hasMarginBeforeQuirk : 1;
  bool m_hasMarginAfterQuirk : 1;
  bool m_determinedMarginBeforeQuirk : 1;

  bool m_discardMargin : 1;
  bool m_lastChildIsSelfCollapsingBlockWithClearance : 1;

  // These flags track the previous maximal positive and negative margins.
  LayoutUnit m_positiveMargin;
  LayoutUnit m_negativeMargin;

 public:
  MarginInfo(LayoutBlockFlow*,
             LayoutUnit beforeBorderPadding,
             LayoutUnit afterBorderPadding);

  void setAtBeforeSideOfBlock(bool b) { m_atBeforeSideOfBlock = b; }
  void setAtAfterSideOfBlock(bool b) { m_atAfterSideOfBlock = b; }
  void clearMargin() {
    m_positiveMargin = LayoutUnit();
    m_negativeMargin = LayoutUnit();
  }
  void setHasMarginBeforeQuirk(bool b) { m_hasMarginBeforeQuirk = b; }
  void setHasMarginAfterQuirk(bool b) { m_hasMarginAfterQuirk = b; }
  void setDeterminedMarginBeforeQuirk(bool b) {
    m_determinedMarginBeforeQuirk = b;
  }
  void setPositiveMargin(LayoutUnit p) {
    ASSERT(!m_discardMargin);
    m_positiveMargin = p;
  }
  void setNegativeMargin(LayoutUnit n) {
    ASSERT(!m_discardMargin);
    m_negativeMargin = n;
  }
  void setPositiveMarginIfLarger(LayoutUnit p) {
    ASSERT(!m_discardMargin);
    if (p > m_positiveMargin)
      m_positiveMargin = p;
  }
  void setNegativeMarginIfLarger(LayoutUnit n) {
    ASSERT(!m_discardMargin);
    if (n > m_negativeMargin)
      m_negativeMargin = n;
  }

  void setMargin(LayoutUnit p, LayoutUnit n) {
    ASSERT(!m_discardMargin);
    m_positiveMargin = p;
    m_negativeMargin = n;
  }
  void setCanCollapseMarginAfterWithChildren(bool collapse) {
    m_canCollapseMarginAfterWithChildren = collapse;
  }
  void setCanCollapseMarginAfterWithLastChild(bool collapse) {
    m_canCollapseMarginAfterWithLastChild = collapse;
  }
  void setDiscardMargin(bool value) { m_discardMargin = value; }

  bool atBeforeSideOfBlock() const { return m_atBeforeSideOfBlock; }
  bool canCollapseWithMarginBefore() const {
    return m_atBeforeSideOfBlock && m_canCollapseMarginBeforeWithChildren;
  }
  bool canCollapseWithMarginAfter() const {
    return m_atAfterSideOfBlock && m_canCollapseMarginAfterWithChildren;
  }
  bool canCollapseMarginBeforeWithChildren() const {
    return m_canCollapseMarginBeforeWithChildren;
  }
  bool canCollapseMarginAfterWithChildren() const {
    return m_canCollapseMarginAfterWithChildren;
  }
  bool canCollapseMarginAfterWithLastChild() const {
    return m_canCollapseMarginAfterWithLastChild;
  }
  bool quirkContainer() const { return m_quirkContainer; }
  bool determinedMarginBeforeQuirk() const {
    return m_determinedMarginBeforeQuirk;
  }
  bool hasMarginBeforeQuirk() const { return m_hasMarginBeforeQuirk; }
  bool hasMarginAfterQuirk() const { return m_hasMarginAfterQuirk; }
  LayoutUnit positiveMargin() const { return m_positiveMargin; }
  LayoutUnit negativeMargin() const { return m_negativeMargin; }
  bool discardMargin() const { return m_discardMargin; }
  LayoutUnit margin() const { return m_positiveMargin - m_negativeMargin; }
  void setLastChildIsSelfCollapsingBlockWithClearance(bool value) {
    m_lastChildIsSelfCollapsingBlockWithClearance = value;
  }
  bool lastChildIsSelfCollapsingBlockWithClearance() const {
    return m_lastChildIsSelfCollapsingBlockWithClearance;
  }
};

// Some features, such as floats, margin collapsing and fragmentation, require
// some knowledge about things that happened when laying out previous block
// child siblings. Only looking at the object currently being laid out isn't
// always enough.
class BlockChildrenLayoutInfo {
 public:
  BlockChildrenLayoutInfo(LayoutBlockFlow* blockFlow,
                          LayoutUnit beforeEdge,
                          LayoutUnit afterEdge)
      : m_marginInfo(blockFlow, beforeEdge, afterEdge),
        m_previousBreakAfterValue(BreakAuto),
        m_isAtFirstInFlowChild(true) {}

  // Store multicol layout state before first layout of a block child. The child
  // may contain a column spanner. If we need to re-lay out the block child
  // because our initial logical top estimate was wrong, we need to roll back to
  // how things were before laying out the child.
  void storeMultiColumnLayoutState(const LayoutFlowThread& flowThread) {
    m_multiColumnLayoutState = flowThread.multiColumnLayoutState();
  }
  void rollBackToInitialMultiColumnLayoutState(LayoutFlowThread& flowThread) {
    flowThread.restoreMultiColumnLayoutState(m_multiColumnLayoutState);
  }

  const MarginInfo& marginInfo() const { return m_marginInfo; }
  MarginInfo& marginInfo() { return m_marginInfo; }
  LayoutUnit& previousFloatLogicalBottom() {
    return m_previousFloatLogicalBottom;
  }

  EBreak previousBreakAfterValue() const { return m_previousBreakAfterValue; }
  void setPreviousBreakAfterValue(EBreak value) {
    m_previousBreakAfterValue = value;
  }

  bool isAtFirstInFlowChild() const { return m_isAtFirstInFlowChild; }
  void clearIsAtFirstInFlowChild() { m_isAtFirstInFlowChild = false; }

 private:
  MultiColumnLayoutState m_multiColumnLayoutState;
  MarginInfo m_marginInfo;
  LayoutUnit m_previousFloatLogicalBottom;
  EBreak m_previousBreakAfterValue;
  bool m_isAtFirstInFlowChild;
};

LayoutBlockFlow::LayoutBlockFlow(ContainerNode* node) : LayoutBlock(node) {
  static_assert(sizeof(MarginInfo) == sizeof(SameSizeAsMarginInfo),
                "MarginInfo should stay small");
  setChildrenInline(true);
}

LayoutBlockFlow::~LayoutBlockFlow() {}

LayoutBlockFlow* LayoutBlockFlow::createAnonymous(Document* document) {
  LayoutBlockFlow* layoutBlockFlow = new LayoutBlockFlow(nullptr);
  layoutBlockFlow->setDocumentForAnonymous(document);
  return layoutBlockFlow;
}

LayoutObject* LayoutBlockFlow::layoutSpecialExcludedChild(
    bool relayoutChildren,
    SubtreeLayoutScope& layoutScope) {
  LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread();
  if (!flowThread)
    return nullptr;
  setLogicalTopForChild(*flowThread, borderBefore() + paddingBefore());
  flowThread->layoutColumns(layoutScope);
  determineLogicalLeftPositionForChild(*flowThread);
  return flowThread;
}

bool LayoutBlockFlow::updateLogicalWidthAndColumnWidth() {
  bool relayoutChildren = LayoutBlock::updateLogicalWidthAndColumnWidth();
  if (LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
    if (flowThread->needsNewWidth())
      return true;
  }
  return relayoutChildren;
}

void LayoutBlockFlow::checkForPaginationLogicalHeightChange(
    LayoutUnit& pageLogicalHeight,
    bool& pageLogicalHeightChanged,
    bool& hasSpecifiedPageLogicalHeight) {
  if (LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
    // Calculate the non-auto content box height, or set it to 0 if it's auto.
    // We need to know this before layout, so that we can figure out where to
    // insert column breaks. We also treat LayoutView (which may be paginated,
    // which uses the multicol implmentation) as having non-auto height, since
    // its height is deduced from the viewport height.
    // We use computeLogicalHeight() to calculate the content box height. That
    // method will clamp against max-height and min-height. Since we're now at
    // the beginning of layout, and we don't know the actual height of the
    // content yet, only call that method when height is definite, or we might
    // fool ourselves into believing that columns have a definite height when
    // they in fact don't.
    LayoutUnit columnHeight;
    if (hasDefiniteLogicalHeight() || isLayoutView()) {
      LogicalExtentComputedValues computedValues;
      computeLogicalHeight(LayoutUnit(), logicalTop(), computedValues);
      columnHeight = computedValues.m_extent - borderAndPaddingLogicalHeight() -
                     scrollbarLogicalHeight();
    }
    pageLogicalHeightChanged =
        columnHeight != flowThread->columnHeightAvailable();
    flowThread->setColumnHeightAvailable(std::max(columnHeight, LayoutUnit()));
  } else if (isLayoutFlowThread()) {
    LayoutFlowThread* flowThread = toLayoutFlowThread(this);

    // FIXME: This is a hack to always make sure we have a page logical height,
    // if said height is known. The page logical height thing in LayoutState is
    // meaningless for flow thread-based pagination (page height isn't
    // necessarily uniform throughout the flow thread), but as long as it is
    // used universally as a means to determine whether page height is known or
    // not, we need this. Page height is unknown when column balancing is
    // enabled and flow thread height is still unknown (i.e. during the first
    // layout pass). When it's unknown, we need to prevent the pagination code
    // from assuming page breaks everywhere and thereby eating every top margin.
    // It should be trivial to clean up and get rid of this hack once the old
    // multicol implementation is gone.
    pageLogicalHeight =
        flowThread->isPageLogicalHeightKnown() ? LayoutUnit(1) : LayoutUnit();

    pageLogicalHeightChanged = flowThread->pageLogicalSizeChanged();
  }
}

void LayoutBlockFlow::setBreakAtLineToAvoidWidow(int lineToBreak) {
  ASSERT(lineToBreak >= 0);
  ensureRareData();
  ASSERT(!m_rareData->m_didBreakAtLineToAvoidWidow);
  m_rareData->m_lineBreakToAvoidWidow = lineToBreak;
}

void LayoutBlockFlow::setDidBreakAtLineToAvoidWidow() {
  ASSERT(!shouldBreakAtLineToAvoidWidow());

  // This function should be called only after a break was applied to avoid
  // widows so assert |m_rareData| exists.
  ASSERT(m_rareData);

  m_rareData->m_didBreakAtLineToAvoidWidow = true;
}

void LayoutBlockFlow::clearDidBreakAtLineToAvoidWidow() {
  if (!m_rareData)
    return;

  m_rareData->m_didBreakAtLineToAvoidWidow = false;
}

void LayoutBlockFlow::clearShouldBreakAtLineToAvoidWidow() const {
  ASSERT(shouldBreakAtLineToAvoidWidow());
  if (!m_rareData)
    return;

  m_rareData->m_lineBreakToAvoidWidow = -1;
}

bool LayoutBlockFlow::isSelfCollapsingBlock() const {
  if (needsLayout()) {
    // Sometimes we don't lay out objects in DOM order (column spanners being
    // one such relevant type of object right here). As long as the object in
    // question establishes a new formatting context, that's nothing to worry
    // about, though.
    ASSERT(createsNewFormattingContext());
    return false;
  }
  ASSERT(!m_isSelfCollapsing == !checkIfIsSelfCollapsingBlock());
  return m_isSelfCollapsing;
}

bool LayoutBlockFlow::checkIfIsSelfCollapsingBlock() const {
  // We are not self-collapsing if we
  // (a) have a non-zero height according to layout (an optimization to avoid
  //     wasting time)
  // (b) have border/padding,
  // (c) have a min-height
  // (d) have specified that one of our margins can't collapse using a CSS
  //     extension
  // (e) establish a new block formatting context.

  // The early exit must be done before we check for clean layout.
  // We should be able to give a quick answer if the box is a relayout boundary.
  // Being a relayout boundary implies a block formatting context, and also
  // our internal layout shouldn't affect our container in any way.
  if (createsNewFormattingContext())
    return false;

  // Placeholder elements are not laid out until the dimensions of their parent
  // text control are known, so they don't get layout until their parent has had
  // layout - this is unique in the layout tree and means when we call
  // isSelfCollapsingBlock on them we find that they still need layout.
  ASSERT(!needsLayout() ||
         (node() && node()->isElementNode() &&
          toElement(node())->shadowPseudoId() == "-webkit-input-placeholder"));

  if (logicalHeight() > LayoutUnit() || borderAndPaddingLogicalHeight() ||
      style()->logicalMinHeight().isPositive() ||
      style()->marginBeforeCollapse() == MarginCollapseSeparate ||
      style()->marginAfterCollapse() == MarginCollapseSeparate)
    return false;

  Length logicalHeightLength = style()->logicalHeight();
  bool hasAutoHeight = logicalHeightLength.isAuto();
  if (logicalHeightLength.isPercentOrCalc() && !document().inQuirksMode()) {
    hasAutoHeight = true;
    for (LayoutBlock* cb = containingBlock(); !cb->isLayoutView();
         cb = cb->containingBlock()) {
      if (cb->style()->logicalHeight().isFixed() || cb->isTableCell())
        hasAutoHeight = false;
    }
  }

  // If the height is 0 or auto, then whether or not we are a self-collapsing
  // block depends on whether we have content that is all self-collapsing.
  // TODO(alancutter): Make this work correctly for calc lengths.
  if (hasAutoHeight || ((logicalHeightLength.isFixed() ||
                         logicalHeightLength.isPercentOrCalc()) &&
                        logicalHeightLength.isZero())) {
    // If the block has inline children, see if we generated any line boxes.
    // If we have any line boxes, then we can't be self-collapsing, since we
    // have content.
    if (childrenInline())
      return !firstLineBox();

    // Whether or not we collapse is dependent on whether all our normal flow
    // children
    // are also self-collapsing.
    for (LayoutBox* child = firstChildBox(); child;
         child = child->nextSiblingBox()) {
      if (child->isFloatingOrOutOfFlowPositioned())
        continue;
      if (!child->isSelfCollapsingBlock())
        return false;
    }
    return true;
  }
  return false;
}

void LayoutBlockFlow::layoutBlock(bool relayoutChildren) {
  ASSERT(needsLayout());
  ASSERT(isInlineBlockOrInlineTable() || !isInline());

  if (!relayoutChildren && simplifiedLayout())
    return;

  LayoutAnalyzer::BlockScope analyzer(*this);
  SubtreeLayoutScope layoutScope(*this);

  // Multiple passes might be required for column based layout.
  // The number of passes could be as high as the number of columns.
  bool done = false;
  LayoutUnit pageLogicalHeight;
  while (!done)
    done = layoutBlockFlow(relayoutChildren, pageLogicalHeight, layoutScope);

  LayoutView* layoutView = view();
  if (layoutView->layoutState()->pageLogicalHeight())
    setPageLogicalOffset(
        layoutView->layoutState()->pageLogicalOffset(*this, logicalTop()));

  updateLayerTransformAfterLayout();

  updateAfterLayout();

  if (isHTMLDialogElement(node()) && isOutOfFlowPositioned())
    positionDialog();

  clearNeedsLayout();
  updateIsSelfCollapsing();
}

DISABLE_CFI_PERF
inline bool LayoutBlockFlow::layoutBlockFlow(bool relayoutChildren,
                                             LayoutUnit& pageLogicalHeight,
                                             SubtreeLayoutScope& layoutScope) {
  LayoutUnit oldLeft = logicalLeft();
  bool logicalWidthChanged = updateLogicalWidthAndColumnWidth();
  relayoutChildren |= logicalWidthChanged;

  rebuildFloatsFromIntruding();

  bool pageLogicalHeightChanged = false;
  bool hasSpecifiedPageLogicalHeight = false;
  checkForPaginationLogicalHeightChange(pageLogicalHeight,
                                        pageLogicalHeightChanged,
                                        hasSpecifiedPageLogicalHeight);
  if (pageLogicalHeightChanged)
    relayoutChildren = true;

  LayoutState state(*this, locationOffset(), pageLogicalHeight,
                    pageLogicalHeightChanged, logicalWidthChanged);

  // We use four values, maxTopPos, maxTopNeg, maxBottomPos, and maxBottomNeg,
  // to track our current maximal positive and negative margins. These values
  // are used when we are collapsed with adjacent blocks, so for example, if you
  // have block A and B collapsing together, then you'd take the maximal
  // positive margin from both A and B and subtract it from the maximal negative
  // margin from both A and B to get the true collapsed margin. This algorithm
  // is recursive, so when we finish layout() our block knows its current
  // maximal positive/negative values.
  //
  // Start out by setting our margin values to our current margins. Table cells
  // have no margins, so we don't fill in the values for table cells.
  if (!isTableCell()) {
    initMaxMarginValues();
    setHasMarginBeforeQuirk(style()->hasMarginBeforeQuirk());
    setHasMarginAfterQuirk(style()->hasMarginAfterQuirk());
  }

  if (state.isPaginated()) {
    setPaginationStrutPropagatedFromChild(LayoutUnit());

    // Start with any applicable computed break-after and break-before values
    // for this object. During child layout, breakBefore will be joined with the
    // breakBefore value of the first in-flow child, and breakAfter will be
    // joined with the breakAfter value of the last in-flow child. This is done
    // in order to honor the requirement that a class A break point [1] may only
    // exists *between* in-flow siblings (i.e. not before the first child and
    // not after the last child).
    //
    // [1] https://drafts.csswg.org/css-break/#possible-breaks
    setBreakBefore(LayoutBlock::breakBefore());
    setBreakAfter(LayoutBlock::breakAfter());
  }

  LayoutUnit beforeEdge = borderBefore() + paddingBefore();
  LayoutUnit afterEdge =
      borderAfter() + paddingAfter() + scrollbarLogicalHeight();
  LayoutUnit previousHeight = logicalHeight();
  setLogicalHeight(beforeEdge);

  if (!firstChild() && !isAnonymousBlock())
    setChildrenInline(true);

  TextAutosizer::LayoutScope textAutosizerLayoutScope(this, &layoutScope);

  bool preferredLogicalWidthsWereDirty = preferredLogicalWidthsDirty();

  // Reset the flag here instead of in layoutInlineChildren() in case that
  // all inline children are removed from this block.
  setContainsInlineWithOutlineAndContinuation(false);
  if (childrenInline())
    layoutInlineChildren(relayoutChildren, afterEdge);
  else
    layoutBlockChildren(relayoutChildren, layoutScope, beforeEdge, afterEdge);

  bool preferredLogicalWidthsBecameDirty =
      !preferredLogicalWidthsWereDirty && preferredLogicalWidthsDirty();
  if (preferredLogicalWidthsBecameDirty) {
    // The only thing that should dirty preferred widths at this point is the
    // addition of overflow:auto scrollbars in a descendant. To avoid a
    // potential infinite loop, run layout again with auto scrollbars frozen in
    // their current state.
    PaintLayerScrollableArea::FreezeScrollbarsScope freezeScrollbars;
    return layoutBlockFlow(relayoutChildren, pageLogicalHeight, layoutScope);
  }

  // Expand our intrinsic height to encompass floats.
  if (lowestFloatLogicalBottom() > (logicalHeight() - afterEdge) &&
      createsNewFormattingContext())
    setLogicalHeight(lowestFloatLogicalBottom() + afterEdge);

  if (LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
    if (flowThread->columnHeightsChanged()) {
      setChildNeedsLayout(MarkOnlyThis);
      return false;
    }
  }

  if (shouldBreakAtLineToAvoidWidow()) {
    setEverHadLayout();
    return false;
  }

  // Calculate our new height.
  LayoutUnit oldHeight = logicalHeight();
  LayoutUnit oldClientAfterEdge = clientLogicalBottom();

  updateLogicalHeight();
  LayoutUnit newHeight = logicalHeight();
  if (!childrenInline()) {
    LayoutBlockFlow* lowestBlock = nullptr;
    bool addedOverhangingFloats = false;
    // One of our children's floats may have become an overhanging float for us.
    for (LayoutObject* child = lastChild(); child;
         child = child->previousSibling()) {
      // TODO(robhogan): We should exclude blocks that create formatting
      // contexts, not just out of flow or floating blocks.
      if (child->isLayoutBlockFlow() &&
          !child->isFloatingOrOutOfFlowPositioned()) {
        LayoutBlockFlow* block = toLayoutBlockFlow(child);
        if (!block->containsFloats())
          continue;
        lowestBlock = block;
        if (oldHeight <= newHeight ||
            block->lowestFloatLogicalBottom() + block->logicalTop() <=
                newHeight)
          break;
        addOverhangingFloats(block, false);
        addedOverhangingFloats = true;
      }
    }
    // If we have no overhanging floats we still pass a record of the lowest
    // non-overhanging float up the tree so we can enclose it if we are a
    // formatting context and allow siblings to avoid it if they have negative
    // margin and find themselves in its vicinity.
    if (!addedOverhangingFloats)
      addLowestFloatFromChildren(lowestBlock);
  }

  bool heightChanged = (previousHeight != newHeight);
  if (heightChanged)
    relayoutChildren = true;

  layoutPositionedObjects(relayoutChildren || isDocumentElement(),
                          oldLeft != logicalLeft()
                              ? ForcedLayoutAfterContainingBlockMoved
                              : DefaultLayout);

  // Add overflow from children (unless we're multi-column, since in that case
  // all our child overflow is clipped anyway).
  computeOverflow(oldClientAfterEdge);

  m_descendantsWithFloatsMarkedForLayout = false;
  return true;
}

void LayoutBlockFlow::addLowestFloatFromChildren(LayoutBlockFlow* block) {
  // TODO(robhogan): Make createsNewFormattingContext an ASSERT.
  if (!block || !block->containsFloats() ||
      block->createsNewFormattingContext())
    return;

  FloatingObject* floatingObject =
      block->m_floatingObjects->lowestFloatingObject();
  if (!floatingObject || containsFloat(floatingObject->layoutObject()))
    return;

  LayoutSize offset(-block->logicalLeft(), -block->logicalTop());
  if (!isHorizontalWritingMode())
    offset = offset.transposedSize();

  if (!m_floatingObjects)
    createFloatingObjects();
  FloatingObject* newFloatingObject = m_floatingObjects->add(
      floatingObject->copyToNewContainer(offset, false, true));
  newFloatingObject->setIsLowestNonOverhangingFloatInChild(true);
}

DISABLE_CFI_PERF
void LayoutBlockFlow::determineLogicalLeftPositionForChild(LayoutBox& child) {
  LayoutUnit startPosition = borderStart() + paddingStart();
  LayoutUnit initialStartPosition = startPosition;
  if (shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
    startPosition -= verticalScrollbarWidth();
  LayoutUnit totalAvailableLogicalWidth =
      borderAndPaddingLogicalWidth() + availableLogicalWidth();

  LayoutUnit childMarginStart = marginStartForChild(child);
  LayoutUnit newPosition = startPosition + childMarginStart;

  if (child.avoidsFloats() && containsFloats()) {
    LayoutUnit positionToAvoidFloats =
        startOffsetForLine(logicalTopForChild(child), DoNotIndentText,
                           logicalHeightForChild(child));

    // If the child has an offset from the content edge to avoid floats then use
    // that, otherwise let any negative margin pull it back over the content
    // edge or any positive margin push it out.
    // If the child is being centred then the margin calculated to do that has
    // factored in any offset required to avoid floats, so use it if necessary.
    if (style()->textAlign() == WEBKIT_CENTER ||
        child.style()->marginStartUsing(style()).isAuto())
      newPosition =
          std::max(newPosition, positionToAvoidFloats + childMarginStart);
    else if (positionToAvoidFloats > initialStartPosition)
      newPosition = std::max(newPosition, positionToAvoidFloats);
  }

  setLogicalLeftForChild(child, style()->isLeftToRightDirection()
                                    ? newPosition
                                    : totalAvailableLogicalWidth - newPosition -
                                          logicalWidthForChild(child));
}

void LayoutBlockFlow::setLogicalLeftForChild(LayoutBox& child,
                                             LayoutUnit logicalLeft) {
  if (isHorizontalWritingMode()) {
    child.setX(logicalLeft);
  } else {
    child.setY(logicalLeft);
  }
}

void LayoutBlockFlow::setLogicalTopForChild(LayoutBox& child,
                                            LayoutUnit logicalTop) {
  if (isHorizontalWritingMode()) {
    child.setY(logicalTop);
  } else {
    child.setX(logicalTop);
  }
}

void LayoutBlockFlow::markDescendantsWithFloatsForLayoutIfNeeded(
    LayoutBlockFlow& child,
    LayoutUnit newLogicalTop,
    LayoutUnit previousFloatLogicalBottom) {
  // TODO(mstensho): rework the code to return early when there is no need for
  // marking, instead of this |markDescendantsWithFloats| flag.
  bool markDescendantsWithFloats = false;
  if (newLogicalTop != child.logicalTop() && !child.avoidsFloats() &&
      child.containsFloats()) {
    markDescendantsWithFloats = true;
  } else if (UNLIKELY(newLogicalTop.mightBeSaturated())) {
    // The logical top might be saturated for very large elements. Comparing
    // with the old logical top might then yield a false negative, as adding and
    // removing margins, borders etc. from a saturated number might yield
    // incorrect results. If this is the case, always mark for layout.
    markDescendantsWithFloats = true;
  } else if (!child.avoidsFloats() || child.shrinkToAvoidFloats()) {
    // If an element might be affected by the presence of floats, then always
    // mark it for layout.
    if (std::max(previousFloatLogicalBottom, lowestFloatLogicalBottom()) >
        newLogicalTop)
      markDescendantsWithFloats = true;
  }

  if (markDescendantsWithFloats)
    child.markAllDescendantsWithFloatsForLayout();
}

bool LayoutBlockFlow::positionAndLayoutOnceIfNeeded(
    LayoutBox& child,
    LayoutUnit newLogicalTop,
    BlockChildrenLayoutInfo& layoutInfo) {
  if (LayoutFlowThread* flowThread = flowThreadContainingBlock())
    layoutInfo.rollBackToInitialMultiColumnLayoutState(*flowThread);

  if (child.isLayoutBlockFlow()) {
    LayoutUnit& previousFloatLogicalBottom =
        layoutInfo.previousFloatLogicalBottom();
    LayoutBlockFlow& childBlockFlow = toLayoutBlockFlow(child);
    if (childBlockFlow.containsFloats() || containsFloats())
      markDescendantsWithFloatsForLayoutIfNeeded(childBlockFlow, newLogicalTop,
                                                 previousFloatLogicalBottom);

    // TODO(mstensho): A writing mode root is one thing, but we should be able
    // to skip anything that establishes a new block formatting context here.
    // Their floats don't affect us.
    if (!childBlockFlow.isWritingModeRoot())
      previousFloatLogicalBottom =
          std::max(previousFloatLogicalBottom,
                   childBlockFlow.logicalTop() +
                       childBlockFlow.lowestFloatLogicalBottom());
  }

  LayoutUnit oldLogicalTop = logicalTopForChild(child);
  setLogicalTopForChild(child, newLogicalTop);

  SubtreeLayoutScope layoutScope(child);
  if (!child.needsLayout()) {
    if (newLogicalTop != oldLogicalTop && child.shrinkToAvoidFloats()) {
      // The child's width is affected by adjacent floats. When the child shifts
      // to clear an item, its width can change (because it has more available
      // width).
      layoutScope.setChildNeedsLayout(&child);
    } else {
      markChildForPaginationRelayoutIfNeeded(child, layoutScope);
    }
  }

  if (!child.needsLayout())
    return false;
  child.layout();
  return true;
}

void LayoutBlockFlow::insertForcedBreakBeforeChildIfNeeded(
    LayoutBox& child,
    BlockChildrenLayoutInfo& layoutInfo) {
  if (layoutInfo.isAtFirstInFlowChild()) {
    // There's no class A break point before the first child (only *between*
    // siblings), so steal its break value and join it with what we already have
    // here.
    setBreakBefore(
        joinFragmentainerBreakValues(breakBefore(), child.breakBefore()));
    return;
  }

  // Figure out if a forced break should be inserted in front of the child. If
  // we insert a forced break, the margins on this child may not collapse with
  // those preceding the break.
  EBreak classABreakPointValue =
      child.classABreakPointValue(layoutInfo.previousBreakAfterValue());
  if (isForcedFragmentainerBreakValue(classABreakPointValue)) {
    layoutInfo.marginInfo().clearMargin();
    LayoutUnit oldLogicalTop = logicalHeight();
    LayoutUnit newLogicalTop =
        applyForcedBreak(oldLogicalTop, classABreakPointValue);
    setLogicalHeight(newLogicalTop);
    LayoutUnit paginationStrut = newLogicalTop - oldLogicalTop;
    child.setPaginationStrut(paginationStrut);
  }
}

void LayoutBlockFlow::layoutBlockChild(LayoutBox& child,
                                       BlockChildrenLayoutInfo& layoutInfo) {
  MarginInfo& marginInfo = layoutInfo.marginInfo();
  LayoutBlockFlow* childLayoutBlockFlow =
      child.isLayoutBlockFlow() ? toLayoutBlockFlow(&child) : nullptr;
  LayoutUnit oldPosMarginBefore = maxPositiveMarginBefore();
  LayoutUnit oldNegMarginBefore = maxNegativeMarginBefore();

  // The child is a normal flow object. Compute the margins we will use for
  // collapsing now.
  child.computeAndSetBlockDirectionMargins(this);

  // Try to guess our correct logical top position. In most cases this guess
  // will be correct. Only if we're wrong (when we compute the real logical top
  // position) will we have to potentially relayout.
  LayoutUnit estimateWithoutPagination;
  LayoutUnit logicalTopEstimate =
      estimateLogicalTopPosition(child, layoutInfo, estimateWithoutPagination);

  // Cache our old rect so that we can dirty the proper paint invalidation rects
  // if the child moves.
  LayoutRect oldRect = child.frameRect();

  if (LayoutFlowThread* flowThread = flowThreadContainingBlock())
    layoutInfo.storeMultiColumnLayoutState(*flowThread);

  // Use the estimated block position and lay out the child if needed. After
  // child layout, when we have enough information to perform proper margin
  // collapsing, float clearing and pagination, we may have to reposition and
  // lay out again if the estimate was wrong.
  bool childNeededLayout =
      positionAndLayoutOnceIfNeeded(child, logicalTopEstimate, layoutInfo);

  // Cache if we are at the top of the block right now.
  bool atBeforeSideOfBlock = marginInfo.atBeforeSideOfBlock();
  bool childIsSelfCollapsing = child.isSelfCollapsingBlock();
  bool childDiscardMarginBefore = mustDiscardMarginBeforeForChild(child);
  bool childDiscardMarginAfter = mustDiscardMarginAfterForChild(child);
  bool paginated = view()->layoutState()->isPaginated();

  // If there should be a forced break before the child, we need to insert it
  // before attempting to collapse margins or apply clearance.
  if (paginated) {
    // We will now insert the strut needed by any forced break. After this
    // operation, we will have calculated the offset where we can apply margin
    // collapsing and clearance. After having applied those things, we'll be at
    // the position where we can honor requirements of unbreakable content,
    // which may extend the strut further.
    child.resetPaginationStrut();
    insertForcedBreakBeforeChildIfNeeded(child, layoutInfo);
  }

  // Now determine the correct ypos based off examination of collapsing margin
  // values.
  LayoutUnit logicalTopBeforeClear =
      collapseMargins(child, marginInfo, childIsSelfCollapsing,
                      childDiscardMarginBefore, childDiscardMarginAfter);

  // Now check for clear.
  bool childDiscardMargin = childDiscardMarginBefore || childDiscardMarginAfter;
  LayoutUnit newLogicalTop = clearFloatsIfNeeded(
      child, marginInfo, oldPosMarginBefore, oldNegMarginBefore,
      logicalTopBeforeClear, childIsSelfCollapsing, childDiscardMargin);

  // If there's a forced break in front of this child, its final position has
  // already been determined. Otherwise, see if there are other reasons for
  // breaking before it (break-inside:avoid, or not enough space for the first
  // piece of child content to fit in the current fragmentainer), and adjust the
  // position accordingly.
  if (paginated) {
    if (estimateWithoutPagination != newLogicalTop) {
      // We got a new position due to clearance or margin collapsing. Before we
      // attempt to paginate (which may result in the position changing again),
      // let's try again at the new position (since a new position may result in
      // a new logical height).
      positionAndLayoutOnceIfNeeded(child, newLogicalTop, layoutInfo);
    }

    // We have now applied forced breaks, margin collapsing and clearance, and
    // we're at the position where we can honor requirements of unbreakable
    // content.
    newLogicalTop = adjustBlockChildForPagination(
        newLogicalTop, child, layoutInfo,
        atBeforeSideOfBlock && logicalTopBeforeClear == newLogicalTop);
  }

  // Clearance, margin collapsing or pagination may have given us a new logical
  // top, in which case we may have to reposition and possibly relayout as well.
  // If we determined during child layout that we need to insert a break to
  // honor widows, we also need to relayout.
  if (newLogicalTop != logicalTopEstimate || child.needsLayout() ||
      (paginated && childLayoutBlockFlow &&
       childLayoutBlockFlow->shouldBreakAtLineToAvoidWidow())) {
    positionAndLayoutOnceIfNeeded(child, newLogicalTop, layoutInfo);
  }

  // If we previously encountered a self-collapsing sibling of this child that
  // had clearance then we set this bit to ensure we would not collapse the
  // child's margins, and those of any subsequent self-collapsing siblings, with
  // our parent. If this child is not self-collapsing then it can collapse its
  // margins with the parent so reset the bit.
  if (!marginInfo.canCollapseMarginAfterWithLastChild() &&
      !childIsSelfCollapsing)
    marginInfo.setCanCollapseMarginAfterWithLastChild(true);

  // We are no longer at the top of the block if we encounter a non-empty child.
  // This has to be done after checking for clear, so that margins can be reset
  // if a clear occurred.
  if (marginInfo.atBeforeSideOfBlock() && !childIsSelfCollapsing)
    marginInfo.setAtBeforeSideOfBlock(false);

  // Now place the child in the correct left position
  determineLogicalLeftPositionForChild(child);

  LayoutSize childOffset = child.location() - oldRect.location();

  // Update our height now that the child has been placed in the correct
  // position.
  setLogicalHeight(logicalHeight() + logicalHeightForChild(child));
  if (mustSeparateMarginAfterForChild(child)) {
    setLogicalHeight(logicalHeight() + marginAfterForChild(child));
    marginInfo.clearMargin();
  }
  // If the child has overhanging floats that intrude into following siblings
  // (or possibly out of this block), then the parent gets notified of the
  // floats now.
  if (childLayoutBlockFlow)
    addOverhangingFloats(childLayoutBlockFlow, !childNeededLayout);

  // If the child moved, we have to invalidate its paint as well as any
  // floating/positioned descendants. An exception is if we need a layout.
  // In this case, we know we're going to invalidate our paint (and the child)
  // anyway.
  if (!selfNeedsLayout() && (childOffset.width() || childOffset.height()) &&
      child.isLayoutBlockFlow())
    BlockFlowPaintInvalidator(toLayoutBlockFlow(child))
        .invalidatePaintForOverhangingFloats();

  if (paginated) {
    // Keep track of the break-after value of the child, so that it can be
    // joined with the break-before value of the next in-flow object at the next
    // class A break point.
    layoutInfo.setPreviousBreakAfterValue(child.breakAfter());

    paginatedContentWasLaidOut(child.logicalBottom());
  }

  if (child.isLayoutMultiColumnSpannerPlaceholder()) {
    // The actual column-span:all element is positioned by this placeholder
    // child.
    positionSpannerDescendant(toLayoutMultiColumnSpannerPlaceholder(child));
  }
}

LayoutUnit LayoutBlockFlow::adjustBlockChildForPagination(
    LayoutUnit logicalTop,
    LayoutBox& child,
    BlockChildrenLayoutInfo& layoutInfo,
    bool atBeforeSideOfBlock) {
  LayoutBlockFlow* childBlockFlow =
      child.isLayoutBlockFlow() ? toLayoutBlockFlow(&child) : 0;

  // See if we need a soft (unforced) break in front of this child, and set the
  // pagination strut in that case. An unforced break may come from two sources:
  // 1. The first piece of content inside the child doesn't fit in the current
  //    page or column
  // 2. The child itself has breaking restrictions (break-inside:avoid, replaced
  //    content, etc.) and doesn't fully fit in the current page or column.
  //
  // No matter which source, if we need to insert a strut, it should always take
  // us to the exact top of a page or column further ahead, or be zero.

  // The first piece of content inside the child may have set a strut during
  // layout. Currently, only block flows support strut propagation, but this may
  // (and should) change in the future. See crbug.com/539873
  LayoutUnit strutFromContent =
      childBlockFlow ? childBlockFlow->paginationStrutPropagatedFromChild()
                     : LayoutUnit();
  LayoutUnit logicalTopWithContentStrut = logicalTop + strutFromContent;

  // For replaced elements and scrolled elements, we want to shift them to the
  // next page if they don't fit on the current one.
  LayoutUnit logicalTopAfterUnsplittable =
      adjustForUnsplittableChild(child, logicalTop);

  // Pick the largest offset. Tall unsplittable content may take us to a page or
  // column further ahead than the next one.
  LayoutUnit logicalTopAfterPagination =
      std::max(logicalTopWithContentStrut, logicalTopAfterUnsplittable);
  LayoutUnit newLogicalTop = logicalTop;

  // Forced breaks may already have caused a strut, and this needs to be added
  // together with any strut detected here in this method.
  LayoutUnit previousStrut = child.paginationStrut();

  if (LayoutUnit paginationStrut =
          logicalTopAfterPagination - logicalTop + previousStrut) {
    ASSERT(paginationStrut > 0);
    // If we're not at the first in-flow child, there's a class A break point
    // before the child. If we *are* at the first in-flow child, but the child
    // isn't flush with the content edge of its container, due to e.g.
    // clearance, there's a class C break point before the child. Otherwise we
    // should propagate the strut to our parent block, and attempt to break
    // there instead. See https://drafts.csswg.org/css-break/#possible-breaks
    if (layoutInfo.isAtFirstInFlowChild() && atBeforeSideOfBlock &&
        allowsPaginationStrut()) {
      // FIXME: Should really check if we're exceeding the page height before
      // propagating the strut, but we don't have all the information to do so
      // (the strut only has the remaining amount to push). Gecko gets this
      // wrong too and pushes to the next page anyway, so not too concerned
      // about it.
      paginationStrut += logicalTop + marginBeforeIfFloating();
      setPaginationStrutPropagatedFromChild(paginationStrut);
      child.resetPaginationStrut();
      if (childBlockFlow)
        childBlockFlow->setPaginationStrutPropagatedFromChild(LayoutUnit());
    } else {
      child.setPaginationStrut(paginationStrut);
      // |previousStrut| was already baked into the logical top, so don't add it
      // again.
      newLogicalTop += paginationStrut - previousStrut;
    }
  }

  // Similar to how we apply clearance. Go ahead and boost height() to be the
  // place where we're going to position the child.
  setLogicalHeight(logicalHeight() + (newLogicalTop - logicalTop));

  // Return the final adjusted logical top.
  return newLogicalTop;
}

static bool shouldSetStrutOnBlock(const LayoutBlockFlow& block,
                                  const RootInlineBox& lineBox,
                                  LayoutUnit lineLogicalOffset,
                                  int lineIndex,
                                  LayoutUnit pageLogicalHeight) {
  if (lineBox == block.firstRootBox()) {
    // This is the first line in the block. We can take the whole block with us
    // to the next page or column, rather than keeping a content-less portion of
    // it in the previous one. Only do this if the line is flush with the
    // content edge of the block, though. If it isn't, it means that the line
    // was pushed downwards by preceding floats that didn't fit beside the line,
    // and we don't want to move all that, since it has already been established
    // that it fits nicely where it is. In this case we have a class "C" break
    // point [1] in front of this line.
    //
    // [1] https://drafts.csswg.org/css-break/#possible-breaks
    if (lineLogicalOffset > block.borderAndPaddingBefore())
      return false;

    LayoutUnit lineHeight =
        lineBox.lineBottomWithLeading() - lineBox.lineTopWithLeading();
    LayoutUnit totalLogicalHeight =
        lineHeight + lineLogicalOffset.clampNegativeToZero();
    // It's rather pointless to break before the block if the current line isn't
    // going to fit in the same column or page, so check that as well.
    if (totalLogicalHeight > pageLogicalHeight)
      return false;
  } else {
    if (lineIndex > block.style()->orphans())
      return false;

    // Not enough orphans here. Push the entire block to the next column / page
    // as an attempt to better satisfy the orphans requirement.
    //
    // Note that we should ideally check if the first line in the block is flush
    // with the content edge of the block here, because if it isn't, we should
    // break at the class "C" break point in front of the first line, rather
    // than before the entire block.
  }
  return block.allowsPaginationStrut();
}

void LayoutBlockFlow::adjustLinePositionForPagination(RootInlineBox& lineBox,
                                                      LayoutUnit& delta) {
  // TODO(mstensho): Pay attention to line overflow. It should be painted in the
  // same column as the rest of the line, possibly overflowing the column. We
  // currently only allow overflow above the first column. We clip at all other
  // column boundaries, and that's how it has to be for now. The paint we have
  // to do when a column has overflow has to be special.
  // We need to exclude content that paints in a previous column (and content
  // that paints in the following column).
  //
  // FIXME: Another problem with simply moving lines is that the available line
  // width may change (because of floats). Technically if the location we move
  // the line to has a different line width than our old position, then we need
  // to dirty the line and all following lines.
  LayoutUnit logicalOffset = lineBox.lineTopWithLeading();
  LayoutUnit lineHeight = lineBox.lineBottomWithLeading() - logicalOffset;
  logicalOffset += delta;
  lineBox.setPaginationStrut(LayoutUnit());
  lineBox.setIsFirstAfterPageBreak(false);
  LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
  if (!pageLogicalHeight)
    return;
  LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(
      logicalOffset, AssociateWithLatterPage);
  int lineIndex = lineCount(&lineBox);
  if (remainingLogicalHeight < lineHeight ||
      (shouldBreakAtLineToAvoidWidow() &&
       lineBreakToAvoidWidow() == lineIndex)) {
    LayoutUnit paginationStrut = calculatePaginationStrutToFitContent(
        logicalOffset, remainingLogicalHeight, lineHeight);
    LayoutUnit newLogicalOffset = logicalOffset + paginationStrut;
    // Moving to a different page or column may mean that its height is
    // different.
    pageLogicalHeight = pageLogicalHeightForOffset(newLogicalOffset);
    if (lineHeight > pageLogicalHeight) {
      // Too tall to fit in one page / column. Give up. Don't push to the next
      // page / column.
      // TODO(mstensho): Get rid of this. This is just utter weirdness, but the
      // other browsers also do something slightly similar, although in much
      // more specific cases than we do here, and printing Google Docs depends
      // on it.
      paginatedContentWasLaidOut(logicalOffset + lineHeight);
      return;
    }

    // We need to insert a break now, either because there's no room for the
    // line in the current column / page, or because we have determined that we
    // need a break to satisfy widow requirements.
    if (shouldBreakAtLineToAvoidWidow() &&
        lineBreakToAvoidWidow() == lineIndex) {
      clearShouldBreakAtLineToAvoidWidow();
      setDidBreakAtLineToAvoidWidow();
    }
    if (shouldSetStrutOnBlock(*this, lineBox, logicalOffset, lineIndex,
                              pageLogicalHeight)) {
      // Note that when setting the strut on a block, it may be propagated to
      // parent blocks later on, if a block's logical top is flush with that of
      // its parent. We don't want content-less portions (struts) at the
      // beginning of a block before a break, if it can be avoided. After all,
      // that's the reason for setting struts on blocks and not lines in the
      // first place.
      LayoutUnit strut =
          paginationStrut + logicalOffset + marginBeforeIfFloating();
      setPaginationStrutPropagatedFromChild(strut);
    } else {
      delta += paginationStrut;
      lineBox.setPaginationStrut(paginationStrut);
      lineBox.setIsFirstAfterPageBreak(true);
    }
    paginatedContentWasLaidOut(newLogicalOffset + lineHeight);
    return;
  }

  LayoutUnit strutToPropagate;
  if (remainingLogicalHeight == pageLogicalHeight) {
    // We're at the very top of a page or column.
    if (lineBox != firstRootBox())
      lineBox.setIsFirstAfterPageBreak(true);
    // If this is the first line in the block, and the block has a top border,
    // padding, or (in case it's a float) margin, we may want to set a strut on
    // the block, so that everything ends up in the next column or page. Setting
    // a strut on the block is also important when it comes to satisfying orphan
    // requirements.
    if (shouldSetStrutOnBlock(*this, lineBox, logicalOffset, lineIndex,
                              pageLogicalHeight))
      strutToPropagate = logicalOffset + marginBeforeIfFloating();
  } else if (lineBox == firstRootBox() && allowsPaginationStrut()) {
    // This is the first line in the block. The block may still start in the
    // previous column or page, and if that's the case, attempt to pull it over
    // to where this line is, so that we don't split the top border, padding, or
    // (in case it's a float) margin.
    LayoutUnit totalLogicalOffset = logicalOffset + marginBeforeIfFloating();
    LayoutUnit strut =
        remainingLogicalHeight + totalLogicalOffset - pageLogicalHeight;
    if (strut > 0) {
      // The block starts in a previous column or page. Set a strut on the block
      // if there's room for the top border, padding and (if it's a float)
      // margin and the line in one column or page.
      if (totalLogicalOffset + lineHeight <= pageLogicalHeight)
        strutToPropagate = strut;
    }
  }

  // If we found that some preceding content (lines, border and padding) belongs
  // together with this line, we should pull the entire block with us to the
  // fragmentainer we're currently in. We need to avoid this when the block
  // precedes the first fragmentainer, though. We shouldn't fragment content
  // there, but rather let it appear in the overflow area before the first
  // fragmentainer.
  if (strutToPropagate && offsetFromLogicalTopOfFirstPage() > LayoutUnit())
    setPaginationStrutPropagatedFromChild(strutToPropagate);

  paginatedContentWasLaidOut(logicalOffset + lineHeight);
}

LayoutUnit LayoutBlockFlow::adjustForUnsplittableChild(
    LayoutBox& child,
    LayoutUnit logicalOffset) const {
  if (child.getPaginationBreakability() == AllowAnyBreaks)
    return logicalOffset;
  LayoutUnit childLogicalHeight = logicalHeightForChild(child);
  // Floats' margins do not collapse with page or column boundaries.
  if (child.isFloating())
    childLogicalHeight +=
        marginBeforeForChild(child) + marginAfterForChild(child);
  LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
  if (!pageLogicalHeight)
    return logicalOffset;
  LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(
      logicalOffset, AssociateWithLatterPage);
  if (remainingLogicalHeight >= childLogicalHeight)
    return logicalOffset;  // It fits fine where it is. No need to break.
  LayoutUnit paginationStrut = calculatePaginationStrutToFitContent(
      logicalOffset, remainingLogicalHeight, childLogicalHeight);
  if (paginationStrut == remainingLogicalHeight &&
      remainingLogicalHeight == pageLogicalHeight) {
    // Don't break if we were at the top of a page, and we failed to fit the
    // content completely. No point in leaving a page completely blank.
    return logicalOffset;
  }
  return logicalOffset + paginationStrut;
}

DISABLE_CFI_PERF
void LayoutBlockFlow::rebuildFloatsFromIntruding() {
  if (m_floatingObjects)
    m_floatingObjects->setHorizontalWritingMode(isHorizontalWritingMode());

  HashSet<LayoutBox*> oldIntrudingFloatSet;
  if (!childrenInline() && m_floatingObjects) {
    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = floatingObjectSet.end();
    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end;
         ++it) {
      const FloatingObject& floatingObject = *it->get();
      if (!floatingObject.isDescendant())
        oldIntrudingFloatSet.add(floatingObject.layoutObject());
    }
  }

  // Inline blocks are covered by the isAtomicInlineLevel() check in the
  // avoidFloats method.
  if (avoidsFloats() || isDocumentElement() || isLayoutView() ||
      isFloatingOrOutOfFlowPositioned() || isTableCell()) {
    if (m_floatingObjects) {
      m_floatingObjects->clear();
    }
    if (!oldIntrudingFloatSet.isEmpty())
      markAllDescendantsWithFloatsForLayout();
    return;
  }

  LayoutBoxToFloatInfoMap floatMap;

  if (m_floatingObjects) {
    if (childrenInline())
      m_floatingObjects->moveAllToFloatInfoMap(floatMap);
    else
      m_floatingObjects->clear();
  }

  // We should not process floats if the parent node is not a LayoutBlockFlow.
  // Otherwise, we will add floats in an invalid context. This will cause a
  // crash arising from a bad cast on the parent.
  // See <rdar://problem/8049753>, where float property is applied on a text
  // node in a SVG.
  if (!parent() || !parent()->isLayoutBlockFlow())
    return;

  // Attempt to locate a previous sibling with overhanging floats. We skip any
  // elements that may have shifted to avoid floats, and any objects whose
  // floats cannot interact with objects outside it (i.e. objects that create a
  // new block formatting context).
  LayoutBlockFlow* parentBlockFlow = toLayoutBlockFlow(parent());
  bool siblingFloatMayIntrude = false;
  LayoutObject* prev = previousSibling();
  while (prev && (!prev->isBox() || !prev->isLayoutBlock() ||
                  toLayoutBlock(prev)->avoidsFloats() ||
                  toLayoutBlock(prev)->createsNewFormattingContext())) {
    if (prev->isFloating())
      siblingFloatMayIntrude = true;
    prev = prev->previousSibling();
  }

  // First add in floats from the parent. Self-collapsing blocks let their
  // parent track any floats that intrude into them (as opposed to floats they
  // contain themselves) so check for those here too. If margin collapsing has
  // moved us up past the top a previous sibling then we need to check for
  // floats from the parent too.
  bool parentFloatsMayIntrude =
      !siblingFloatMayIntrude &&
      (!prev || toLayoutBlockFlow(prev)->isSelfCollapsingBlock() ||
       toLayoutBlock(prev)->logicalTop() > logicalTop()) &&
      parentBlockFlow->lowestFloatLogicalBottom() > logicalTop();
  if (siblingFloatMayIntrude || parentFloatsMayIntrude)
    addIntrudingFloats(parentBlockFlow,
                       parentBlockFlow->logicalLeftOffsetForContent(),
                       logicalTop());

  // Add overhanging floats from the previous LayoutBlockFlow, but only if it
  // has a float that intrudes into our space.
  if (prev) {
    LayoutBlockFlow* previousBlockFlow = toLayoutBlockFlow(prev);
    if (logicalTop() < previousBlockFlow->logicalTop() +
                           previousBlockFlow->lowestFloatLogicalBottom())
      addIntrudingFloats(previousBlockFlow, LayoutUnit(),
                         logicalTop() - previousBlockFlow->logicalTop());
  }

  if (childrenInline()) {
    LayoutUnit changeLogicalTop = LayoutUnit::max();
    LayoutUnit changeLogicalBottom = LayoutUnit::min();
    if (m_floatingObjects) {
      const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
      FloatingObjectSetIterator end = floatingObjectSet.end();
      for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end;
           ++it) {
        const FloatingObject& floatingObject = *it->get();
        FloatingObject* oldFloatingObject =
            floatMap.get(floatingObject.layoutObject());
        LayoutUnit logicalBottom = logicalBottomForFloat(floatingObject);
        if (oldFloatingObject) {
          LayoutUnit oldLogicalBottom =
              logicalBottomForFloat(*oldFloatingObject);
          if (logicalWidthForFloat(floatingObject) !=
                  logicalWidthForFloat(*oldFloatingObject) ||
              logicalLeftForFloat(floatingObject) !=
                  logicalLeftForFloat(*oldFloatingObject)) {
            changeLogicalTop = LayoutUnit();
            changeLogicalBottom = std::max(
                changeLogicalBottom, std::max(logicalBottom, oldLogicalBottom));
          } else {
            if (logicalBottom != oldLogicalBottom) {
              changeLogicalTop = std::min(
                  changeLogicalTop, std::min(logicalBottom, oldLogicalBottom));
              changeLogicalBottom =
                  std::max(changeLogicalBottom,
                           std::max(logicalBottom, oldLogicalBottom));
            }
            LayoutUnit logicalTop = logicalTopForFloat(floatingObject);
            LayoutUnit oldLogicalTop = logicalTopForFloat(*oldFloatingObject);
            if (logicalTop != oldLogicalTop) {
              changeLogicalTop = std::min(changeLogicalTop,
                                          std::min(logicalTop, oldLogicalTop));
              changeLogicalBottom = std::max(
                  changeLogicalBottom, std::max(logicalTop, oldLogicalTop));
            }
          }

          if (oldFloatingObject->originatingLine() && !selfNeedsLayout()) {
            ASSERT(oldFloatingObject->originatingLine()
                       ->getLineLayoutItem()
                       .isEqual(this));
            oldFloatingObject->originatingLine()->markDirty();
          }

          floatMap.remove(floatingObject.layoutObject());
        } else {
          changeLogicalTop = LayoutUnit();
          changeLogicalBottom = std::max(changeLogicalBottom, logicalBottom);
        }
      }
    }

    LayoutBoxToFloatInfoMap::iterator end = floatMap.end();
    for (LayoutBoxToFloatInfoMap::iterator it = floatMap.begin(); it != end;
         ++it) {
      std::unique_ptr<FloatingObject>& floatingObject = it->value;
      if (!floatingObject->isDescendant()) {
        changeLogicalTop = LayoutUnit();
        changeLogicalBottom = std::max(changeLogicalBottom,
                                       logicalBottomForFloat(*floatingObject));
      }
    }

    markLinesDirtyInBlockRange(changeLogicalTop, changeLogicalBottom);
  } else if (!oldIntrudingFloatSet.isEmpty()) {
    // If there are previously intruding floats that no longer intrude, then
    // children with floats should also get layout because they might need their
    // floating object lists cleared.
    if (m_floatingObjects->set().size() < oldIntrudingFloatSet.size()) {
      markAllDescendantsWithFloatsForLayout();
    } else {
      const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
      FloatingObjectSetIterator end = floatingObjectSet.end();
      for (FloatingObjectSetIterator it = floatingObjectSet.begin();
           it != end && !oldIntrudingFloatSet.isEmpty(); ++it)
        oldIntrudingFloatSet.remove((*it)->layoutObject());
      if (!oldIntrudingFloatSet.isEmpty())
        markAllDescendantsWithFloatsForLayout();
    }
  }
}

void LayoutBlockFlow::layoutBlockChildren(bool relayoutChildren,
                                          SubtreeLayoutScope& layoutScope,
                                          LayoutUnit beforeEdge,
                                          LayoutUnit afterEdge) {
  dirtyForLayoutFromPercentageHeightDescendants(layoutScope);

  BlockChildrenLayoutInfo layoutInfo(this, beforeEdge, afterEdge);
  MarginInfo& marginInfo = layoutInfo.marginInfo();

  LayoutObject* childToExclude =
      layoutSpecialExcludedChild(relayoutChildren, layoutScope);

  // TODO(foolip): Speculative CHECKs to crash if any non-LayoutBox
  // children ever appear, the childrenInline() check at the call site
  // should make this impossible. crbug.com/632848
  LayoutObject* firstChild = this->firstChild();
  CHECK(!firstChild || firstChild->isBox());
  LayoutBox* next = toLayoutBox(firstChild);
  LayoutBox* lastNormalFlowChild = nullptr;

  while (next) {
    LayoutBox* child = next;
    LayoutObject* nextSibling = child->nextSibling();
    CHECK(!nextSibling || nextSibling->isBox());
    next = toLayoutBox(nextSibling);

    child->setMayNeedPaintInvalidation();

    if (childToExclude == child)
      continue;  // Skip this child, since it will be positioned by the
                 // specialized subclass (ruby runs).

    updateBlockChildDirtyBitsBeforeLayout(relayoutChildren, *child);

    if (child->isOutOfFlowPositioned()) {
      child->containingBlock()->insertPositionedObject(child);
      adjustPositionedBlock(*child, layoutInfo);
      continue;
    }
    if (child->isFloating()) {
      insertFloatingObject(*child);
      adjustFloatingBlock(marginInfo);
      continue;
    }
    if (child->isColumnSpanAll()) {
      // This is not the containing block of the spanner. The spanner's
      // placeholder will lay it out in due course. For now we just need to
      // consult our flow thread, so that the columns (if any) preceding and
      // following the spanner are laid out correctly. But first we apply the
      // pending margin, so that it's taken into consideration and doesn't end
      // up on the other side of the spanner.
      setLogicalHeight(logicalHeight() + marginInfo.margin());
      marginInfo.clearMargin();

      child->spannerPlaceholder()->flowThread()->skipColumnSpanner(
          child, offsetFromLogicalTopOfFirstPage() + logicalHeight());
      continue;
    }

    // Lay out the child.
    layoutBlockChild(*child, layoutInfo);
    layoutInfo.clearIsAtFirstInFlowChild();
    lastNormalFlowChild = child;
  }

  // Now do the handling of the bottom of the block, adding in our bottom
  // border/padding and determining the correct collapsed bottom margin
  // information.
  handleAfterSideOfBlock(lastNormalFlowChild, beforeEdge, afterEdge,
                         marginInfo);
}

// Our MarginInfo state used when laying out block children.
MarginInfo::MarginInfo(LayoutBlockFlow* blockFlow,
                       LayoutUnit beforeBorderPadding,
                       LayoutUnit afterBorderPadding)
    : m_canCollapseMarginAfterWithLastChild(true),
      m_atBeforeSideOfBlock(true),
      m_atAfterSideOfBlock(false),
      m_hasMarginBeforeQuirk(false),
      m_hasMarginAfterQuirk(false),
      m_determinedMarginBeforeQuirk(false),
      m_discardMargin(false),
      m_lastChildIsSelfCollapsingBlockWithClearance(false) {
  const ComputedStyle& blockStyle = blockFlow->styleRef();
  ASSERT(blockFlow->isLayoutView() || blockFlow->parent());
  m_canCollapseWithChildren = !blockFlow->createsNewFormattingContext() &&
                              !blockFlow->isLayoutFlowThread() &&
                              !blockFlow->isLayoutView();

  m_canCollapseMarginBeforeWithChildren =
      m_canCollapseWithChildren && !beforeBorderPadding &&
      blockStyle.marginBeforeCollapse() != MarginCollapseSeparate;

  // If any height other than auto is specified in CSS, then we don't collapse
  // our bottom margins with our children's margins. To do otherwise would be to
  // risk odd visual effects when the children overflow out of the parent block
  // and yet still collapse with it. We also don't collapse if we have any
  // bottom border/padding.
  m_canCollapseMarginAfterWithChildren =
      m_canCollapseWithChildren && !afterBorderPadding &&
      (blockStyle.logicalHeight().isAuto() &&
       !blockStyle.logicalHeight().value()) &&
      blockStyle.marginAfterCollapse() != MarginCollapseSeparate;

  m_quirkContainer = blockFlow->isTableCell() || blockFlow->isBody();

  m_discardMargin = m_canCollapseMarginBeforeWithChildren &&
                    blockFlow->mustDiscardMarginBefore();

  m_positiveMargin = (m_canCollapseMarginBeforeWithChildren &&
                      !blockFlow->mustDiscardMarginBefore())
                         ? blockFlow->maxPositiveMarginBefore()
                         : LayoutUnit();
  m_negativeMargin = (m_canCollapseMarginBeforeWithChildren &&
                      !blockFlow->mustDiscardMarginBefore())
                         ? blockFlow->maxNegativeMarginBefore()
                         : LayoutUnit();
}

LayoutBlockFlow::MarginValues LayoutBlockFlow::marginValuesForChild(
    LayoutBox& child) const {
  LayoutUnit childBeforePositive;
  LayoutUnit childBeforeNegative;
  LayoutUnit childAfterPositive;
  LayoutUnit childAfterNegative;

  LayoutUnit beforeMargin;
  LayoutUnit afterMargin;

  LayoutBlockFlow* childLayoutBlockFlow =
      child.isLayoutBlockFlow() ? toLayoutBlockFlow(&child) : 0;

  // If the child has the same directionality as we do, then we can just return
  // its margins in the same direction.
  if (!child.isWritingModeRoot()) {
    if (childLayoutBlockFlow) {
      childBeforePositive = childLayoutBlockFlow->maxPositiveMarginBefore();
      childBeforeNegative = childLayoutBlockFlow->maxNegativeMarginBefore();
      childAfterPositive = childLayoutBlockFlow->maxPositiveMarginAfter();
      childAfterNegative = childLayoutBlockFlow->maxNegativeMarginAfter();
    } else {
      beforeMargin = child.marginBefore();
      afterMargin = child.marginAfter();
    }
  } else if (child.isHorizontalWritingMode() == isHorizontalWritingMode()) {
    // The child has a different directionality. If the child is parallel, then
    // it's just flipped relative to us. We can use the margins for the opposite
    // edges.
    if (childLayoutBlockFlow) {
      childBeforePositive = childLayoutBlockFlow->maxPositiveMarginAfter();
      childBeforeNegative = childLayoutBlockFlow->maxNegativeMarginAfter();
      childAfterPositive = childLayoutBlockFlow->maxPositiveMarginBefore();
      childAfterNegative = childLayoutBlockFlow->maxNegativeMarginBefore();
    } else {
      beforeMargin = child.marginAfter();
      afterMargin = child.marginBefore();
    }
  } else {
    // The child is perpendicular to us, which means its margins don't collapse
    // but are on the "logical left/right" sides of the child box. We can just
    // return the raw margin in this case.
    beforeMargin = marginBeforeForChild(child);
    afterMargin = marginAfterForChild(child);
  }

  // Resolve uncollapsing margins into their positive/negative buckets.
  if (beforeMargin) {
    if (beforeMargin > 0)
      childBeforePositive = beforeMargin;
    else
      childBeforeNegative = -beforeMargin;
  }
  if (afterMargin) {
    if (afterMargin > 0)
      childAfterPositive = afterMargin;
    else
      childAfterNegative = -afterMargin;
  }

  return LayoutBlockFlow::MarginValues(childBeforePositive, childBeforeNegative,
                                       childAfterPositive, childAfterNegative);
}

LayoutUnit LayoutBlockFlow::collapseMargins(LayoutBox& child,
                                            MarginInfo& marginInfo,
                                            bool childIsSelfCollapsing,
                                            bool childDiscardMarginBefore,
                                            bool childDiscardMarginAfter) {
  // The child discards the before margin when the the after margin has discard
  // in the case of a self collapsing block.
  childDiscardMarginBefore = childDiscardMarginBefore ||
                             (childDiscardMarginAfter && childIsSelfCollapsing);

  // Get the four margin values for the child and cache them.
  const LayoutBlockFlow::MarginValues childMargins =
      marginValuesForChild(child);

  // Get our max pos and neg top margins.
  LayoutUnit posTop = childMargins.positiveMarginBefore();
  LayoutUnit negTop = childMargins.negativeMarginBefore();

  // For self-collapsing blocks, collapse our bottom margins into our
  // top to get new posTop and negTop values.
  if (childIsSelfCollapsing) {
    posTop = std::max(posTop, childMargins.positiveMarginAfter());
    negTop = std::max(negTop, childMargins.negativeMarginAfter());
  }

  // See if the top margin is quirky. We only care if this child has
  // margins that will collapse with us.
  bool topQuirk = hasMarginBeforeQuirk(&child);

  if (marginInfo.canCollapseWithMarginBefore()) {
    if (!childDiscardMarginBefore && !marginInfo.discardMargin()) {
      // This child is collapsing with the top of the
      // block. If it has larger margin values, then we need to update
      // our own maximal values.
      if (!document().inQuirksMode() || !marginInfo.quirkContainer() ||
          !topQuirk)
        setMaxMarginBeforeValues(std::max(posTop, maxPositiveMarginBefore()),
                                 std::max(negTop, maxNegativeMarginBefore()));

      // The minute any of the margins involved isn't a quirk, don't
      // collapse it away, even if the margin is smaller (www.webreference.com
      // has an example of this, a <dt> with 0.8em author-specified inside
      // a <dl> inside a <td>.
      if (!marginInfo.determinedMarginBeforeQuirk() && !topQuirk &&
          (posTop - negTop)) {
        setHasMarginBeforeQuirk(false);
        marginInfo.setDeterminedMarginBeforeQuirk(true);
      }

      if (!marginInfo.determinedMarginBeforeQuirk() && topQuirk &&
          !marginBefore()) {
        // We have no top margin and our top child has a quirky margin.
        // We will pick up this quirky margin and pass it through.
        // This deals with the <td><div><p> case.
        // Don't do this for a block that split two inlines though. You do
        // still apply margins in this case.
        setHasMarginBeforeQuirk(true);
      }
    } else {
      // The before margin of the container will also discard all the margins it
      // is collapsing with.
      setMustDiscardMarginBefore();
    }
  }

  // Once we find a child with discardMarginBefore all the margins collapsing
  // with us must also discard.
  if (childDiscardMarginBefore) {
    marginInfo.setDiscardMargin(true);
    marginInfo.clearMargin();
  }

  if (marginInfo.quirkContainer() && marginInfo.atBeforeSideOfBlock() &&
      (posTop - negTop))
    marginInfo.setHasMarginBeforeQuirk(topQuirk);

  LayoutUnit beforeCollapseLogicalTop = logicalHeight();
  LayoutUnit logicalTop = beforeCollapseLogicalTop;

  LayoutObject* prev = child.previousSibling();
  LayoutBlockFlow* previousBlockFlow =
      prev && prev->isLayoutBlockFlow() &&
              !prev->isFloatingOrOutOfFlowPositioned()
          ? toLayoutBlockFlow(prev)
          : 0;
  // If the child's previous sibling is a self-collapsing block that cleared a
  // float then its top border edge has been set at the bottom border edge of
  // the float. Since we want to collapse the child's top margin with the self-
  // collapsing block's top and bottom margins we need to adjust our parent's
  // height to match the margin top of the self-collapsing block. If the
  // resulting collapsed margin leaves the child still intruding into the float
  // then we will want to clear it.
  if (!marginInfo.canCollapseWithMarginBefore() && previousBlockFlow &&
      marginInfo.lastChildIsSelfCollapsingBlockWithClearance())
    setLogicalHeight(
        logicalHeight() -
        marginValuesForChild(*previousBlockFlow).positiveMarginBefore());

  if (childIsSelfCollapsing) {
    // For a self collapsing block both the before and after margins get
    // discarded. The block doesn't contribute anything to the height of the
    // block. Also, the child's top position equals the logical height of the
    // container.
    if (!childDiscardMarginBefore && !marginInfo.discardMargin()) {
      // This child has no height. We need to compute our
      // position before we collapse the child's margins together,
      // so that we can get an accurate position for the zero-height block.
      LayoutUnit collapsedBeforePos = std::max(
          marginInfo.positiveMargin(), childMargins.positiveMarginBefore());
      LayoutUnit collapsedBeforeNeg = std::max(
          marginInfo.negativeMargin(), childMargins.negativeMarginBefore());
      marginInfo.setMargin(collapsedBeforePos, collapsedBeforeNeg);

      // Now collapse the child's margins together, which means examining our
      // bottom margin values as well.
      marginInfo.setPositiveMarginIfLarger(childMargins.positiveMarginAfter());
      marginInfo.setNegativeMarginIfLarger(childMargins.negativeMarginAfter());

      if (!marginInfo.canCollapseWithMarginBefore()) {
        // We need to make sure that the position of the self-collapsing block
        // is correct, since it could have overflowing content
        // that needs to be positioned correctly (e.g., a block that
        // had a specified height of 0 but that actually had subcontent).
        logicalTop = logicalHeight() + collapsedBeforePos - collapsedBeforeNeg;
      }
    }
  } else {
    if (mustSeparateMarginBeforeForChild(child)) {
      ASSERT(!marginInfo.discardMargin() ||
             (marginInfo.discardMargin() && !marginInfo.margin()));
      // If we are at the before side of the block and we collapse, ignore the
      // computed margin and just add the child margin to the container height.
      // This will correctly position the child inside the container.
      LayoutUnit separateMargin = !marginInfo.canCollapseWithMarginBefore()
                                      ? marginInfo.margin()
                                      : LayoutUnit();
      setLogicalHeight(logicalHeight() + separateMargin +
                       marginBeforeForChild(child));
      logicalTop = logicalHeight();
    } else if (!marginInfo.discardMargin() &&
               (!marginInfo.atBeforeSideOfBlock() ||
                (!marginInfo.canCollapseMarginBeforeWithChildren() &&
                 (!document().inQuirksMode() || !marginInfo.quirkContainer() ||
                  !marginInfo.hasMarginBeforeQuirk())))) {
      // We're collapsing with a previous sibling's margins and not
      // with the top of the block.
      setLogicalHeight(logicalHeight() +
                       std::max(marginInfo.positiveMargin(), posTop) -
                       std::max(marginInfo.negativeMargin(), negTop));
      logicalTop = logicalHeight();
    }

    marginInfo.setDiscardMargin(childDiscardMarginAfter);

    if (!marginInfo.discardMargin()) {
      marginInfo.setPositiveMargin(childMargins.positiveMarginAfter());
      marginInfo.setNegativeMargin(childMargins.negativeMarginAfter());
    } else {
      marginInfo.clearMargin();
    }

    if (marginInfo.margin())
      marginInfo.setHasMarginAfterQuirk(hasMarginAfterQuirk(&child));
  }

  // If margins would pull us past the top of the next page, then we need to
  // pull back and pretend like the margins collapsed into the page edge.
  LayoutState* layoutState = view()->layoutState();
  if (layoutState->isPaginated() &&
      isPageLogicalHeightKnown(beforeCollapseLogicalTop) &&
      logicalTop > beforeCollapseLogicalTop) {
    LayoutUnit oldLogicalTop = logicalTop;
    logicalTop =
        std::min(logicalTop, nextPageLogicalTop(beforeCollapseLogicalTop));
    setLogicalHeight(logicalHeight() + (logicalTop - oldLogicalTop));
  }

  if (previousBlockFlow) {
    // If |child| is a self-collapsing block it may have collapsed into a
    // previous sibling and although it hasn't reduced the height of the parent
    // yet any floats from the parent will now overhang.
    LayoutUnit oldLogicalHeight = logicalHeight();
    setLogicalHeight(logicalTop);
    if (!previousBlockFlow->avoidsFloats() &&
        (previousBlockFlow->logicalTop() +
         previousBlockFlow->lowestFloatLogicalBottom()) > logicalTop)
      addOverhangingFloats(previousBlockFlow, false);
    setLogicalHeight(oldLogicalHeight);

    // If |child|'s previous sibling is or contains a self-collapsing block that
    // cleared a float and margin collapsing resulted in |child| moving up
    // into the margin area of the self-collapsing block then the float it
    // clears is now intruding into |child|. Layout again so that we can look
    // for floats in the parent that overhang |child|'s new logical top.
    bool logicalTopIntrudesIntoFloat = logicalTop < beforeCollapseLogicalTop;
    if (logicalTopIntrudesIntoFloat && containsFloats() &&
        !child.avoidsFloats() && lowestFloatLogicalBottom() > logicalTop)
      child.setNeedsLayoutAndFullPaintInvalidation(
          LayoutInvalidationReason::AncestorMarginCollapsing);
  }

  return logicalTop;
}

void LayoutBlockFlow::adjustPositionedBlock(
    LayoutBox& child,
    const BlockChildrenLayoutInfo& layoutInfo) {
  LayoutUnit logicalTop = logicalHeight();

  // Forced breaks are only specified on in-flow objects, but auto-positioned
  // out-of-flow objects may be affected by a break-after value of the previous
  // in-flow object.
  if (view()->layoutState()->isPaginated())
    logicalTop =
        applyForcedBreak(logicalTop, layoutInfo.previousBreakAfterValue());

  updateStaticInlinePositionForChild(child, logicalTop);

  const MarginInfo& marginInfo = layoutInfo.marginInfo();
  if (!marginInfo.canCollapseWithMarginBefore()) {
    // Positioned blocks don't collapse margins, so add the margin provided by
    // the container now. The child's own margin is added later when calculating
    // its logical top.
    LayoutUnit collapsedBeforePos = marginInfo.positiveMargin();
    LayoutUnit collapsedBeforeNeg = marginInfo.negativeMargin();
    logicalTop += collapsedBeforePos - collapsedBeforeNeg;
  }

  PaintLayer* childLayer = child.layer();
  if (childLayer->staticBlockPosition() != logicalTop)
    childLayer->setStaticBlockPosition(logicalTop);
}

LayoutUnit LayoutBlockFlow::clearFloatsIfNeeded(LayoutBox& child,
                                                MarginInfo& marginInfo,
                                                LayoutUnit oldTopPosMargin,
                                                LayoutUnit oldTopNegMargin,
                                                LayoutUnit yPos,
                                                bool childIsSelfCollapsing,
                                                bool childDiscardMargin) {
  LayoutUnit heightIncrease = getClearDelta(&child, yPos);
  marginInfo.setLastChildIsSelfCollapsingBlockWithClearance(false);

  if (!heightIncrease)
    return yPos;

  if (childIsSelfCollapsing) {
    marginInfo.setLastChildIsSelfCollapsingBlockWithClearance(true);
    marginInfo.setDiscardMargin(childDiscardMargin);

    // For self-collapsing blocks that clear, they can still collapse their
    // margins with following siblings. Reset the current margins to represent
    // the self-collapsing block's margins only.
    // If DISCARD is specified for -webkit-margin-collapse, reset the margin
    // values.
    LayoutBlockFlow::MarginValues childMargins = marginValuesForChild(child);
    if (!childDiscardMargin) {
      marginInfo.setPositiveMargin(
          std::max(childMargins.positiveMarginBefore(),
                   childMargins.positiveMarginAfter()));
      marginInfo.setNegativeMargin(
          std::max(childMargins.negativeMarginBefore(),
                   childMargins.negativeMarginAfter()));
    } else {
      marginInfo.clearMargin();
    }

    // CSS2.1 states:
    // "If the top and bottom margins of an element with clearance are
    // adjoining, its margins collapse with the adjoining margins of following
    // siblings but that resulting margin does not collapse with the bottom
    // margin of the parent block."
    // So the parent's bottom margin cannot collapse through this block or any
    // subsequent self-collapsing blocks. Set a bit to ensure this happens; it
    // will get reset if we encounter an in-flow sibling that is not
    // self-collapsing.
    marginInfo.setCanCollapseMarginAfterWithLastChild(false);

    // For now set the border-top of |child| flush with the bottom border-edge
    // of the float so it can layout any floating or positioned children of its
    // own at the correct vertical position. If subsequent siblings attempt to
    // collapse with |child|'s margins in |collapseMargins| we will adjust the
    // height of the parent to |child|'s margin top (which if it is positive
    // sits up 'inside' the float it's clearing) so that all three margins can
    // collapse at the correct vertical position.
    // Per CSS2.1 we need to ensure that any negative margin-top clears |child|
    // beyond the bottom border-edge of the float so that the top border edge of
    // the child (i.e. its clearance)  is at a position that satisfies the
    // equation: "the amount of clearance is set so that:
    //   clearance + margin-top = [height of float],
    // i.e., clearance = [height of float] - margin-top".
    setLogicalHeight(child.logicalTop() + childMargins.negativeMarginBefore());
  } else {
    // Increase our height by the amount we had to clear.
    setLogicalHeight(logicalHeight() + heightIncrease);
  }

  if (marginInfo.canCollapseWithMarginBefore()) {
    // We can no longer collapse with the top of the block since a clear
    // occurred. The empty blocks collapse into the cleared block.
    setMaxMarginBeforeValues(oldTopPosMargin, oldTopNegMargin);
    marginInfo.setAtBeforeSideOfBlock(false);

    // In case the child discarded the before margin of the block we need to
    // reset the mustDiscardMarginBefore flag to the initial value.
    setMustDiscardMarginBefore(style()->marginBeforeCollapse() ==
                               MarginCollapseDiscard);
  }

  return yPos + heightIncrease;
}

void LayoutBlockFlow::setCollapsedBottomMargin(const MarginInfo& marginInfo) {
  if (marginInfo.canCollapseWithMarginAfter() &&
      !marginInfo.canCollapseWithMarginBefore()) {
    // Update the after side margin of the container to discard if the after
    // margin of the last child also discards and we collapse with it.
    // Don't update the max margin values because we won't need them anyway.
    if (marginInfo.discardMargin()) {
      setMustDiscardMarginAfter();
      return;
    }

    // Update our max pos/neg bottom margins, since we collapsed our bottom
    // margins with our children.
    setMaxMarginAfterValues(
        std::max(maxPositiveMarginAfter(), marginInfo.positiveMargin()),
        std::max(maxNegativeMarginAfter(), marginInfo.negativeMargin()));

    if (!marginInfo.hasMarginAfterQuirk())
      setHasMarginAfterQuirk(false);

    if (marginInfo.hasMarginAfterQuirk() && !marginAfter()) {
      // We have no bottom margin and our last child has a quirky margin.
      // We will pick up this quirky margin and pass it through.
      // This deals with the <td><div><p> case.
      setHasMarginAfterQuirk(true);
    }
  }
}

DISABLE_CFI_PERF
void LayoutBlockFlow::marginBeforeEstimateForChild(
    LayoutBox& child,
    LayoutUnit& positiveMarginBefore,
    LayoutUnit& negativeMarginBefore,
    bool& discardMarginBefore) const {
  // Give up if in quirks mode and we're a body/table cell and the top margin of
  // the child box is quirky.
  // Give up if the child specified -webkit-margin-collapse: separate that
  // prevents collapsing.
  // FIXME: Use writing mode independent accessor for marginBeforeCollapse.
  if ((document().inQuirksMode() && hasMarginBeforeQuirk(&child) &&
       (isTableCell() || isBody())) ||
      child.style()->marginBeforeCollapse() == MarginCollapseSeparate)
    return;

  // The margins are discarded by a child that specified
  // -webkit-margin-collapse: discard.
  // FIXME: Use writing mode independent accessor for marginBeforeCollapse.
  if (child.style()->marginBeforeCollapse() == MarginCollapseDiscard) {
    positiveMarginBefore = LayoutUnit();
    negativeMarginBefore = LayoutUnit();
    discardMarginBefore = true;
    return;
  }

  LayoutUnit beforeChildMargin = marginBeforeForChild(child);
  positiveMarginBefore = std::max(positiveMarginBefore, beforeChildMargin);
  negativeMarginBefore = std::max(negativeMarginBefore, -beforeChildMargin);

  if (!child.isLayoutBlockFlow())
    return;

  LayoutBlockFlow* childBlockFlow = toLayoutBlockFlow(&child);
  if (childBlockFlow->childrenInline() || childBlockFlow->isWritingModeRoot())
    return;

  MarginInfo childMarginInfo(
      childBlockFlow,
      childBlockFlow->borderBefore() + childBlockFlow->paddingBefore(),
      childBlockFlow->borderAfter() + childBlockFlow->paddingAfter());
  if (!childMarginInfo.canCollapseMarginBeforeWithChildren())
    return;

  LayoutBox* grandchildBox = childBlockFlow->firstChildBox();
  for (; grandchildBox; grandchildBox = grandchildBox->nextSiblingBox()) {
    if (!grandchildBox->isFloatingOrOutOfFlowPositioned() &&
        !grandchildBox->isColumnSpanAll())
      break;
  }

  if (!grandchildBox)
    return;

  // Make sure to update the block margins now for the grandchild box so that
  // we're looking at current values.
  if (grandchildBox->needsLayout()) {
    grandchildBox->computeAndSetBlockDirectionMargins(this);
    if (grandchildBox->isLayoutBlock()) {
      LayoutBlock* grandchildBlock = toLayoutBlock(grandchildBox);
      grandchildBlock->setHasMarginBeforeQuirk(
          grandchildBox->style()->hasMarginBeforeQuirk());
      grandchildBlock->setHasMarginAfterQuirk(
          grandchildBox->style()->hasMarginAfterQuirk());
    }
  }

  // If we have a 'clear' value but also have a margin we may not actually
  // require clearance to move past any floats. If that's the case we want to be
  // sure we estimate the correct position including margins after any floats
  // rather than use 'clearance' later which could give us the wrong position.
  if (grandchildBox->style()->clear() != ClearNone &&
      childBlockFlow->marginBeforeForChild(*grandchildBox) == 0)
    return;

  // Collapse the margin of the grandchild box with our own to produce an
  // estimate.
  childBlockFlow->marginBeforeEstimateForChild(
      *grandchildBox, positiveMarginBefore, negativeMarginBefore,
      discardMarginBefore);
}

LayoutUnit LayoutBlockFlow::estimateLogicalTopPosition(
    LayoutBox& child,
    const BlockChildrenLayoutInfo& layoutInfo,
    LayoutUnit& estimateWithoutPagination) {
  const MarginInfo& marginInfo = layoutInfo.marginInfo();
  // FIXME: We need to eliminate the estimation of vertical position, because
  // when it's wrong we sometimes trigger a pathological
  // relayout if there are intruding floats.
  LayoutUnit logicalTopEstimate = logicalHeight();
  LayoutUnit positiveMarginBefore;
  LayoutUnit negativeMarginBefore;
  bool discardMarginBefore = false;
  if (!marginInfo.canCollapseWithMarginBefore()) {
    if (child.selfNeedsLayout()) {
      // Try to do a basic estimation of how the collapse is going to go.
      marginBeforeEstimateForChild(child, positiveMarginBefore,
                                   negativeMarginBefore, discardMarginBefore);
    } else {
      // Use the cached collapsed margin values from a previous layout. Most of
      // the time they will be right.
      LayoutBlockFlow::MarginValues marginValues = marginValuesForChild(child);
      positiveMarginBefore =
          std::max(positiveMarginBefore, marginValues.positiveMarginBefore());
      negativeMarginBefore =
          std::max(negativeMarginBefore, marginValues.negativeMarginBefore());
      discardMarginBefore = mustDiscardMarginBeforeForChild(child);
    }

    // Collapse the result with our current margins.
    if (!discardMarginBefore)
      logicalTopEstimate +=
          std::max(marginInfo.positiveMargin(), positiveMarginBefore) -
          std::max(marginInfo.negativeMargin(), negativeMarginBefore);
  }

  // Adjust logicalTopEstimate down to the next page if the margins are so large
  // that we don't fit on the current page.
  LayoutState* layoutState = view()->layoutState();
  if (layoutState->isPaginated() && isPageLogicalHeightKnown(logicalHeight()) &&
      logicalTopEstimate > logicalHeight())
    logicalTopEstimate =
        std::min(logicalTopEstimate, nextPageLogicalTop(logicalHeight()));

  logicalTopEstimate += getClearDelta(&child, logicalTopEstimate);

  estimateWithoutPagination = logicalTopEstimate;

  if (layoutState->isPaginated()) {
    if (!layoutInfo.isAtFirstInFlowChild()) {
      // Estimate the need for a forced break in front of this child. The final
      // break policy at this class A break point isn't known until we have laid
      // out the children of |child|. There may be forced break-before values
      // set on first-children inside that get propagated up to the child.
      // Just make an estimate with what we know so far.
      EBreak breakValue =
          child.classABreakPointValue(layoutInfo.previousBreakAfterValue());
      if (isForcedFragmentainerBreakValue(breakValue)) {
        logicalTopEstimate = applyForcedBreak(logicalHeight(), breakValue);
        // Disregard previous margins, since they will collapse with the
        // fragmentainer boundary, due to the forced break. Only apply margins
        // that have been specified on the child or its descendants.
        if (!discardMarginBefore)
          logicalTopEstimate += positiveMarginBefore - negativeMarginBefore;

        // Clearance may already have taken us past the beginning of the next
        // fragmentainer.
        return std::max(estimateWithoutPagination, logicalTopEstimate);
      }
    }

    // For replaced elements and scrolled elements, we want to shift them to the
    // next page if they don't fit on the current one.
    logicalTopEstimate = adjustForUnsplittableChild(child, logicalTopEstimate);
  }

  return logicalTopEstimate;
}

void LayoutBlockFlow::adjustFloatingBlock(const MarginInfo& marginInfo) {
  // The float should be positioned taking into account the bottom margin
  // of the previous flow. We add that margin into the height, get the
  // float positioned properly, and then subtract the margin out of the
  // height again. In the case of self-collapsing blocks, we always just
  // use the top margins, since the self-collapsing block collapsed its
  // own bottom margin into its top margin.
  //
  // Note also that the previous flow may collapse its margin into the top of
  // our block. If this is the case, then we do not add the margin in to our
  // height when computing the position of the float. This condition can be
  // tested for by simply calling canCollapseWithMarginBefore. See
  // http://www.hixie.ch/tests/adhoc/css/box/block/margin-collapse/046.html for
  // an example of this scenario.
  LayoutUnit marginOffset = marginInfo.canCollapseWithMarginBefore()
                                ? LayoutUnit()
                                : marginInfo.margin();
  setLogicalHeight(logicalHeight() + marginOffset);
  positionNewFloats();
  setLogicalHeight(logicalHeight() - marginOffset);
}

void LayoutBlockFlow::handleAfterSideOfBlock(LayoutBox* lastChild,
                                             LayoutUnit beforeSide,
                                             LayoutUnit afterSide,
                                             MarginInfo& marginInfo) {
  marginInfo.setAtAfterSideOfBlock(true);

  // If our last child was a self-collapsing block with clearance then our
  // logical height is flush with the bottom edge of the float that the child
  // clears. The correct vertical position for the margin-collapsing we want to
  // perform now is at the child's margin-top - so adjust our height to that
  // position.
  if (marginInfo.lastChildIsSelfCollapsingBlockWithClearance()) {
    ASSERT(lastChild);
    setLogicalHeight(logicalHeight() -
                     marginValuesForChild(*lastChild).positiveMarginBefore());
  }

  if (marginInfo.canCollapseMarginAfterWithChildren() &&
      !marginInfo.canCollapseMarginAfterWithLastChild())
    marginInfo.setCanCollapseMarginAfterWithChildren(false);

  // If we can't collapse with children then go ahead and add in the bottom
  // margin.
  if (!marginInfo.discardMargin() &&
      (!marginInfo.canCollapseWithMarginAfter() &&
       !marginInfo.canCollapseWithMarginBefore() &&
       (!document().inQuirksMode() || !marginInfo.quirkContainer() ||
        !marginInfo.hasMarginAfterQuirk())))
    setLogicalHeight(logicalHeight() + marginInfo.margin());

  // Now add in our bottom border/padding.
  setLogicalHeight(logicalHeight() + afterSide);

  // Negative margins can cause our height to shrink below our minimal height
  // (border/padding). If this happens, ensure that the computed height is
  // increased to the minimal height.
  setLogicalHeight(std::max(logicalHeight(), beforeSide + afterSide));

  // Update our bottom collapsed margin info.
  setCollapsedBottomMargin(marginInfo);

  // There's no class A break point right after the last child, only *between*
  // siblings. So propagate the break-after value, and keep looking for a class
  // A break point (at the next in-flow block-level object), where we'll join
  // this break-after value with the break-before value there.
  if (view()->layoutState()->isPaginated() && lastChild)
    setBreakAfter(
        joinFragmentainerBreakValues(breakAfter(), lastChild->breakAfter()));
}

void LayoutBlockFlow::setMustDiscardMarginBefore(bool value) {
  if (style()->marginBeforeCollapse() == MarginCollapseDiscard) {
    ASSERT(value);
    return;
  }

  if (!m_rareData && !value)
    return;

  if (!m_rareData)
    m_rareData = wrapUnique(new LayoutBlockFlowRareData(this));

  m_rareData->m_discardMarginBefore = value;
}

void LayoutBlockFlow::setMustDiscardMarginAfter(bool value) {
  if (style()->marginAfterCollapse() == MarginCollapseDiscard) {
    ASSERT(value);
    return;
  }

  if (!m_rareData && !value)
    return;

  if (!m_rareData)
    m_rareData = wrapUnique(new LayoutBlockFlowRareData(this));

  m_rareData->m_discardMarginAfter = value;
}

bool LayoutBlockFlow::mustDiscardMarginBefore() const {
  return style()->marginBeforeCollapse() == MarginCollapseDiscard ||
         (m_rareData && m_rareData->m_discardMarginBefore);
}

bool LayoutBlockFlow::mustDiscardMarginAfter() const {
  return style()->marginAfterCollapse() == MarginCollapseDiscard ||
         (m_rareData && m_rareData->m_discardMarginAfter);
}

bool LayoutBlockFlow::mustDiscardMarginBeforeForChild(
    const LayoutBox& child) const {
  ASSERT(!child.selfNeedsLayout());
  if (!child.isWritingModeRoot())
    return child.isLayoutBlockFlow()
               ? toLayoutBlockFlow(&child)->mustDiscardMarginBefore()
               : (child.style()->marginBeforeCollapse() ==
                  MarginCollapseDiscard);
  if (child.isHorizontalWritingMode() == isHorizontalWritingMode())
    return child.isLayoutBlockFlow()
               ? toLayoutBlockFlow(&child)->mustDiscardMarginAfter()
               : (child.style()->marginAfterCollapse() ==
                  MarginCollapseDiscard);

  // FIXME: We return false here because the implementation is not geometrically
  // complete. We have values only for before/after, not start/end.
  // In case the boxes are perpendicular we assume the property is not
  // specified.
  return false;
}

bool LayoutBlockFlow::mustDiscardMarginAfterForChild(
    const LayoutBox& child) const {
  ASSERT(!child.selfNeedsLayout());
  if (!child.isWritingModeRoot())
    return child.isLayoutBlockFlow()
               ? toLayoutBlockFlow(&child)->mustDiscardMarginAfter()
               : (child.style()->marginAfterCollapse() ==
                  MarginCollapseDiscard);
  if (child.isHorizontalWritingMode() == isHorizontalWritingMode())
    return child.isLayoutBlockFlow()
               ? toLayoutBlockFlow(&child)->mustDiscardMarginBefore()
               : (child.style()->marginBeforeCollapse() ==
                  MarginCollapseDiscard);

  // FIXME: See |mustDiscardMarginBeforeForChild| above.
  return false;
}

void LayoutBlockFlow::setMaxMarginBeforeValues(LayoutUnit pos, LayoutUnit neg) {
  if (!m_rareData) {
    if (pos == LayoutBlockFlowRareData::positiveMarginBeforeDefault(this) &&
        neg == LayoutBlockFlowRareData::negativeMarginBeforeDefault(this))
      return;
    m_rareData = wrapUnique(new LayoutBlockFlowRareData(this));
  }
  m_rareData->m_margins.setPositiveMarginBefore(pos);
  m_rareData->m_margins.setNegativeMarginBefore(neg);
}

void LayoutBlockFlow::setMaxMarginAfterValues(LayoutUnit pos, LayoutUnit neg) {
  if (!m_rareData) {
    if (pos == LayoutBlockFlowRareData::positiveMarginAfterDefault(this) &&
        neg == LayoutBlockFlowRareData::negativeMarginAfterDefault(this))
      return;
    m_rareData = wrapUnique(new LayoutBlockFlowRareData(this));
  }
  m_rareData->m_margins.setPositiveMarginAfter(pos);
  m_rareData->m_margins.setNegativeMarginAfter(neg);
}

bool LayoutBlockFlow::mustSeparateMarginBeforeForChild(
    const LayoutBox& child) const {
  ASSERT(!child.selfNeedsLayout());
  const ComputedStyle& childStyle = child.styleRef();
  if (!child.isWritingModeRoot())
    return childStyle.marginBeforeCollapse() == MarginCollapseSeparate;
  if (child.isHorizontalWritingMode() == isHorizontalWritingMode())
    return childStyle.marginAfterCollapse() == MarginCollapseSeparate;

  // FIXME: See |mustDiscardMarginBeforeForChild| above.
  return false;
}

bool LayoutBlockFlow::mustSeparateMarginAfterForChild(
    const LayoutBox& child) const {
  ASSERT(!child.selfNeedsLayout());
  const ComputedStyle& childStyle = child.styleRef();
  if (!child.isWritingModeRoot())
    return childStyle.marginAfterCollapse() == MarginCollapseSeparate;
  if (child.isHorizontalWritingMode() == isHorizontalWritingMode())
    return childStyle.marginBeforeCollapse() == MarginCollapseSeparate;

  // FIXME: See |mustDiscardMarginBeforeForChild| above.
  return false;
}

LayoutUnit LayoutBlockFlow::applyForcedBreak(LayoutUnit logicalOffset,
                                             EBreak breakValue) {
  if (!isForcedFragmentainerBreakValue(breakValue))
    return logicalOffset;
  // TODO(mstensho): honor breakValue. There are different types of forced
  // breaks. We currently just assume that we want to break to the top of the
  // next fragmentainer of the fragmentation context we're in. However, we may
  // want to find the next left or right page - even if we're inside a multicol
  // container when printing.
  LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
  if (!pageLogicalHeight)
    return logicalOffset;  // Page height is still unknown, so we cannot insert
                           // forced breaks.
  LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(
      logicalOffset, AssociateWithLatterPage);
  if (remainingLogicalHeight == pageLogicalHeight)
    return logicalOffset;  // Don't break if we're already at the block start of
                           // a fragmentainer.
  return logicalOffset + remainingLogicalHeight;
}

void LayoutBlockFlow::setBreakBefore(EBreak breakValue) {
  if (breakValue != BreakAuto && !isBreakBetweenControllable(breakValue))
    breakValue = BreakAuto;
  if (breakValue == BreakAuto && !m_rareData)
    return;
  ensureRareData().m_breakBefore = breakValue;
}

void LayoutBlockFlow::setBreakAfter(EBreak breakValue) {
  if (breakValue != BreakAuto && !isBreakBetweenControllable(breakValue))
    breakValue = BreakAuto;
  if (breakValue == BreakAuto && !m_rareData)
    return;
  ensureRareData().m_breakAfter = breakValue;
}

EBreak LayoutBlockFlow::breakBefore() const {
  return m_rareData ? static_cast<EBreak>(m_rareData->m_breakBefore)
                    : BreakAuto;
}

EBreak LayoutBlockFlow::breakAfter() const {
  return m_rareData ? static_cast<EBreak>(m_rareData->m_breakAfter) : BreakAuto;
}

void LayoutBlockFlow::addOverflowFromFloats() {
  if (!m_floatingObjects)
    return;

  const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
  FloatingObjectSetIterator end = floatingObjectSet.end();
  for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end;
       ++it) {
    const FloatingObject& floatingObject = *it->get();
    if (floatingObject.isDescendant())
      addOverflowFromChild(
          floatingObject.layoutObject(),
          LayoutSize(xPositionForFloatIncludingMargin(floatingObject),
                     yPositionForFloatIncludingMargin(floatingObject)));
  }
}

void LayoutBlockFlow::computeOverflow(LayoutUnit oldClientAfterEdge,
                                      bool recomputeFloats) {
  LayoutBlock::computeOverflow(oldClientAfterEdge, recomputeFloats);
  if (recomputeFloats || createsNewFormattingContext() ||
      hasSelfPaintingLayer())
    addOverflowFromFloats();
}

void LayoutBlockFlow::computeSelfHitTestRects(
    Vector<LayoutRect>& rects,
    const LayoutPoint& layerOffset) const {
  LayoutBlock::computeSelfHitTestRects(rects, layerOffset);

  if (!hasHorizontalLayoutOverflow() && !hasVerticalLayoutOverflow())
    return;

  for (RootInlineBox* curr = firstRootBox(); curr; curr = curr->nextRootBox()) {
    LayoutUnit top = std::max<LayoutUnit>(curr->lineTop(), curr->top());
    LayoutUnit bottom =
        std::min<LayoutUnit>(curr->lineBottom(), curr->top() + curr->height());
    LayoutRect rect(layerOffset.x() + curr->x(), layerOffset.y() + top,
                    curr->width(), bottom - top);
    // It's common for this rect to be entirely contained in our box, so exclude
    // that simple case.
    if (!rect.isEmpty() && (rects.isEmpty() || !rects[0].contains(rect)))
      rects.append(rect);
  }
}

void LayoutBlockFlow::absoluteRects(
    Vector<IntRect>& rects,
    const LayoutPoint& accumulatedOffset) const {
  if (!isAnonymousBlockContinuation()) {
    LayoutBlock::absoluteRects(rects, accumulatedOffset);
    return;
  }
  // For blocks inside inlines, we go ahead and include margins so that we run
  // right up to the inline boxes above and below us (thus getting merged with
  // them to form a single irregular shape).
  // FIXME: This is wrong for vertical writing-modes.
  // https://bugs.webkit.org/show_bug.cgi?id=46781
  LayoutRect rect(accumulatedOffset, size());
  rect.expand(collapsedMarginBoxLogicalOutsets());
  rects.append(pixelSnappedIntRect(rect));
  continuation()->absoluteRects(
      rects,
      accumulatedOffset -
          toLayoutSize(
              location() +
              inlineElementContinuation()->containingBlock()->location()));
}

void LayoutBlockFlow::absoluteQuads(Vector<FloatQuad>& quads) const {
  if (!isAnonymousBlockContinuation()) {
    LayoutBlock::absoluteQuads(quads);
    return;
  }
  // For blocks inside inlines, we go ahead and include margins so that we run
  // right up to the inline boxes above and below us (thus getting merged with
  // them to form a single irregular shape).
  // FIXME: This is wrong for vertical writing-modes.
  // https://bugs.webkit.org/show_bug.cgi?id=46781
  LayoutRect localRect(LayoutPoint(), size());
  localRect.expand(collapsedMarginBoxLogicalOutsets());
  quads.append(localToAbsoluteQuad(FloatRect(localRect)));
  continuation()->absoluteQuads(quads);
}

LayoutObject* LayoutBlockFlow::hoverAncestor() const {
  return isAnonymousBlockContinuation() ? continuation()
                                        : LayoutBlock::hoverAncestor();
}

RootInlineBox* LayoutBlockFlow::createAndAppendRootInlineBox() {
  RootInlineBox* rootBox = createRootInlineBox();
  m_lineBoxes.appendLineBox(rootBox);

  return rootBox;
}

void LayoutBlockFlow::deleteLineBoxTree() {
  if (containsFloats())
    m_floatingObjects->clearLineBoxTreePointers();

  m_lineBoxes.deleteLineBoxTree();
}

int LayoutBlockFlow::lineCount(const RootInlineBox* stopRootInlineBox) const {
#ifndef NDEBUG
  ASSERT(!stopRootInlineBox ||
         stopRootInlineBox->block().debugPointer() == this);
#endif
  if (!childrenInline())
    return 0;

  int count = 0;
  for (const RootInlineBox* box = firstRootBox(); box;
       box = box->nextRootBox()) {
    count++;
    if (box == stopRootInlineBox)
      break;
  }
  return count;
}

int LayoutBlockFlow::firstLineBoxBaseline() const {
  if (isWritingModeRoot() && !isRubyRun())
    return -1;
  if (!childrenInline())
    return LayoutBlock::firstLineBoxBaseline();
  if (firstLineBox())
    return (firstLineBox()->logicalTop() +
            style(true)->getFontMetrics().ascent(
                firstRootBox()->baselineType()))
        .toInt();
  return -1;
}

int LayoutBlockFlow::inlineBlockBaseline(
    LineDirectionMode lineDirection) const {
  // CSS2.1 states that the baseline of an 'inline-block' is:
  // the baseline of the last line box in the normal flow, unless it has
  // either no in-flow line boxes or if its 'overflow' property has a computed
  // value other than 'visible', in which case the baseline is the bottom
  // margin edge.
  // We likewise avoid using the last line box in the case of size containment,
  // where the block's contents shouldn't be considered when laying out its
  // ancestors or siblings.

  if ((!style()->isOverflowVisible() &&
       !shouldIgnoreOverflowPropertyForInlineBlockBaseline()) ||
      style()->containsSize()) {
    // We are not calling baselinePosition here because the caller should add
    // the margin-top/margin-right, not us.
    return (lineDirection == HorizontalLine ? size().height() + marginBottom()
                                            : size().width() + marginLeft())
        .toInt();
  }
  if (isWritingModeRoot() && !isRubyRun())
    return -1;
  if (!childrenInline())
    return LayoutBlock::inlineBlockBaseline(lineDirection);
  if (lastLineBox())
    return (lastLineBox()->logicalTop() +
            style(lastLineBox() == firstLineBox())
                ->getFontMetrics()
                .ascent(lastRootBox()->baselineType()))
        .toInt();
  if (!hasLineIfEmpty())
    return -1;
  const FontMetrics& fontMetrics = firstLineStyle()->getFontMetrics();
  return (fontMetrics.ascent() +
          (lineHeight(true, lineDirection, PositionOfInteriorLineBoxes) -
           fontMetrics.height()) /
              2 +
          (lineDirection == HorizontalLine ? borderTop() + paddingTop()
                                           : borderRight() + paddingRight()))
      .toInt();
}

void LayoutBlockFlow::removeFloatingObjectsFromDescendants() {
  if (!containsFloats())
    return;
  removeFloatingObjects();
  setChildNeedsLayout(MarkOnlyThis);

  // If our children are inline, then the only boxes which could contain floats
  // are atomic inlines (e.g. inline-block, float etc.) and these create
  // formatting contexts, so can't pick up intruding floats from
  // ancestors/siblings - making them safe to skip.
  if (childrenInline())
    return;
  for (LayoutObject* child = firstChild(); child;
       child = child->nextSibling()) {
    // We don't skip blocks that create formatting contexts as they may have
    // only recently changed style and their float lists may still contain
    // floats from siblings and ancestors.
    if (child->isLayoutBlockFlow())
      toLayoutBlockFlow(child)->removeFloatingObjectsFromDescendants();
  }
}

void LayoutBlockFlow::markAllDescendantsWithFloatsForLayout(
    LayoutBox* floatToRemove,
    bool inLayout) {
  if (!everHadLayout() && !containsFloats())
    return;

  if (m_descendantsWithFloatsMarkedForLayout && !floatToRemove)
    return;
  m_descendantsWithFloatsMarkedForLayout |= !floatToRemove;

  MarkingBehavior markParents = inLayout ? MarkOnlyThis : MarkContainerChain;
  setChildNeedsLayout(markParents);

  if (floatToRemove)
    removeFloatingObject(floatToRemove);

  // Iterate over our children and mark them as needed. If our children are
  // inline, then the only boxes which could contain floats are atomic inlines
  // (e.g. inline-block, float etc.) and these create formatting contexts, so
  // can't pick up intruding floats from ancestors/siblings - making them safe
  // to skip.
  if (!childrenInline()) {
    for (LayoutObject* child = firstChild(); child;
         child = child->nextSibling()) {
      if ((!floatToRemove && child->isFloatingOrOutOfFlowPositioned()) ||
          !child->isLayoutBlock())
        continue;
      if (!child->isLayoutBlockFlow()) {
        LayoutBlock* childBlock = toLayoutBlock(child);
        if (childBlock->shrinkToAvoidFloats() && childBlock->everHadLayout())
          childBlock->setChildNeedsLayout(markParents);
        continue;
      }
      LayoutBlockFlow* childBlockFlow = toLayoutBlockFlow(child);
      if ((floatToRemove ? childBlockFlow->containsFloat(floatToRemove)
                         : childBlockFlow->containsFloats()) ||
          childBlockFlow->shrinkToAvoidFloats())
        childBlockFlow->markAllDescendantsWithFloatsForLayout(floatToRemove,
                                                              inLayout);
    }
  }
}

void LayoutBlockFlow::markSiblingsWithFloatsForLayout(
    LayoutBox* floatToRemove) {
  if (!m_floatingObjects)
    return;

  const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
  FloatingObjectSetIterator end = floatingObjectSet.end();

  for (LayoutObject* next = nextSibling(); next; next = next->nextSibling()) {
    if (!next->isLayoutBlockFlow() ||
        (!floatToRemove && (next->isFloatingOrOutOfFlowPositioned() ||
                            toLayoutBlockFlow(next)->avoidsFloats())))
      continue;

    LayoutBlockFlow* nextBlock = toLayoutBlockFlow(next);
    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end;
         ++it) {
      LayoutBox* floatingBox = (*it)->layoutObject();
      if (floatToRemove && floatingBox != floatToRemove)
        continue;
      if (nextBlock->containsFloat(floatingBox))
        nextBlock->markAllDescendantsWithFloatsForLayout(floatingBox);
    }
  }
}

LayoutUnit LayoutBlockFlow::getClearDelta(LayoutBox* child,
                                          LayoutUnit logicalTop) {
  // There is no need to compute clearance if we have no floats.
  if (!containsFloats())
    return LayoutUnit();

  // At least one float is present. We need to perform the clearance
  // computation.
  bool clearSet = child->style()->clear() != ClearNone;
  LayoutUnit logicalBottom;
  switch (child->style()->clear()) {
    case ClearNone:
      break;
    case ClearLeft:
      logicalBottom = lowestFloatLogicalBottom(FloatingObject::FloatLeft);
      break;
    case ClearRight:
      logicalBottom = lowestFloatLogicalBottom(FloatingObject::FloatRight);
      break;
    case ClearBoth:
      logicalBottom = lowestFloatLogicalBottom();
      break;
  }

  // We also clear floats if we are too big to sit on the same line as a float
  // (and wish to avoid floats by default).
  LayoutUnit result = clearSet
                          ? (logicalBottom - logicalTop).clampNegativeToZero()
                          : LayoutUnit();
  if (!result && child->avoidsFloats()) {
    LayoutUnit newLogicalTop = logicalTop;
    LayoutRect borderBox = child->borderBoxRect();
    LayoutUnit childLogicalWidthAtOldLogicalTopOffset =
        isHorizontalWritingMode() ? borderBox.width() : borderBox.height();
    while (true) {
      LayoutUnit availableLogicalWidthAtNewLogicalTopOffset =
          availableLogicalWidthForLine(newLogicalTop, DoNotIndentText,
                                       logicalHeightForChild(*child));
      if (availableLogicalWidthAtNewLogicalTopOffset ==
          availableLogicalWidthForContent())
        return newLogicalTop - logicalTop;

      LogicalExtentComputedValues computedValues;
      child->logicalExtentAfterUpdatingLogicalWidth(newLogicalTop,
                                                    computedValues);
      LayoutUnit childLogicalWidthAtNewLogicalTopOffset =
          computedValues.m_extent;

      if (childLogicalWidthAtNewLogicalTopOffset <=
          availableLogicalWidthAtNewLogicalTopOffset) {
        // Even though we may not be moving, if the logical width did shrink
        // because of the presence of new floats, then we need to force a
        // relayout as though we shifted. This happens because of the dynamic
        // addition of overhanging floats from previous siblings when negative
        // margins exist on a child (see the addOverhangingFloats call at the
        // end of collapseMargins).
        if (childLogicalWidthAtOldLogicalTopOffset !=
            childLogicalWidthAtNewLogicalTopOffset)
          child->setChildNeedsLayout(MarkOnlyThis);
        return newLogicalTop - logicalTop;
      }

      newLogicalTop = nextFloatLogicalBottomBelowForBlock(newLogicalTop);
      ASSERT(newLogicalTop >= logicalTop);
      if (newLogicalTop < logicalTop)
        break;
    }
    ASSERT_NOT_REACHED();
  }
  return result;
}

void LayoutBlockFlow::createFloatingObjects() {
  m_floatingObjects =
      wrapUnique(new FloatingObjects(this, isHorizontalWritingMode()));
}

void LayoutBlockFlow::willBeDestroyed() {
  // Mark as being destroyed to avoid trouble with merges in removeChild().
  m_beingDestroyed = true;

  // Make sure to destroy anonymous children first while they are still
  // connected to the rest of the tree, so that they will properly dirty line
  // boxes that they are removed from. Effects that do :before/:after only on
  // hover could crash otherwise.
  children()->destroyLeftoverChildren();

  // Destroy our continuation before anything other than anonymous children.
  // The reason we don't destroy it before anonymous children is that they may
  // have continuations of their own that are anonymous children of our
  // continuation.
  LayoutBoxModelObject* continuation = this->continuation();
  if (continuation) {
    continuation->destroy();
    setContinuation(nullptr);
  }

  if (!documentBeingDestroyed()) {
    // TODO(mstensho): figure out if we need this. We have no test coverage for
    // it. It looks like all line boxes have been removed at this point.
    if (firstLineBox()) {
      // We can't wait for LayoutBox::destroy to clear the selection,
      // because by then we will have nuked the line boxes.
      // FIXME: The FrameSelection should be responsible for this when it
      // is notified of DOM mutations.
      if (isSelectionBorder())
        view()->clearSelection();

      // If we are an anonymous block, then our line boxes might have children
      // that will outlast this block. In the non-anonymous block case those
      // children will be destroyed by the time we return from this function.
      if (isAnonymousBlock()) {
        for (InlineFlowBox* box = firstLineBox(); box;
             box = box->nextLineBox()) {
          while (InlineBox* childBox = box->firstChild())
            childBox->remove();
        }
      }
    }
  }

  m_lineBoxes.deleteLineBoxes();

  LayoutBlock::willBeDestroyed();
}

void LayoutBlockFlow::styleWillChange(StyleDifference diff,
                                      const ComputedStyle& newStyle) {
  const ComputedStyle* oldStyle = style();
  s_canPropagateFloatIntoSibling =
      oldStyle ? !isFloatingOrOutOfFlowPositioned() && !avoidsFloats() : false;
  if (oldStyle && parent() && diff.needsFullLayout() &&
      oldStyle->position() != newStyle.position() && containsFloats() &&
      !isFloating() && !isOutOfFlowPositioned() &&
      newStyle.hasOutOfFlowPosition())
    markAllDescendantsWithFloatsForLayout();

  LayoutBlock::styleWillChange(diff, newStyle);
}

DISABLE_CFI_PERF
void LayoutBlockFlow::styleDidChange(StyleDifference diff,
                                     const ComputedStyle* oldStyle) {
  bool hadSelfPaintingLayer = hasSelfPaintingLayer();
  LayoutBlock::styleDidChange(diff, oldStyle);

  // After our style changed, if we lose our ability to propagate floats into
  // next sibling blocks, then we need to find the top most parent containing
  // that overhanging float and then mark its descendants with floats for layout
  // and clear all floats from its next sibling blocks that exist in our
  // floating objects list. See crbug.com/56299 and crbug.com/62875.
  bool canPropagateFloatIntoSibling =
      !isFloatingOrOutOfFlowPositioned() && !avoidsFloats();
  bool siblingFloatPropagationChanged =
      diff.needsFullLayout() && s_canPropagateFloatIntoSibling &&
      !canPropagateFloatIntoSibling && hasOverhangingFloats();

  // When this object's self-painting layer status changed, we should update
  // FloatingObjects::shouldPaint() flags for descendant overhanging floats in
  // ancestors.
  bool needsUpdateAncestorFloatObjectShouldPaintFlags = false;
  if (hasSelfPaintingLayer() != hadSelfPaintingLayer &&
      hasOverhangingFloats()) {
    setNeedsLayout(LayoutInvalidationReason::StyleChange);
    if (hadSelfPaintingLayer)
      markAllDescendantsWithFloatsForLayout();
    else
      needsUpdateAncestorFloatObjectShouldPaintFlags = true;
  }

  if (siblingFloatPropagationChanged ||
      needsUpdateAncestorFloatObjectShouldPaintFlags) {
    LayoutBlockFlow* parentBlockFlow = this;
    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = floatingObjectSet.end();

    for (LayoutObject* curr = parent(); curr && !curr->isLayoutView();
         curr = curr->parent()) {
      if (curr->isLayoutBlockFlow()) {
        LayoutBlockFlow* currBlock = toLayoutBlockFlow(curr);

        if (currBlock->hasOverhangingFloats()) {
          for (FloatingObjectSetIterator it = floatingObjectSet.begin();
               it != end; ++it) {
            LayoutBox* layoutBox = (*it)->layoutObject();
            if (currBlock->hasOverhangingFloat(layoutBox)) {
              parentBlockFlow = currBlock;
              break;
            }
          }
        }
      }
    }

    parentBlockFlow->markAllDescendantsWithFloatsForLayout();
    if (siblingFloatPropagationChanged)
      parentBlockFlow->markSiblingsWithFloatsForLayout();
  }

  if (diff.needsFullLayout() || !oldStyle)
    createOrDestroyMultiColumnFlowThreadIfNeeded(oldStyle);
  if (oldStyle) {
    if (LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
      if (!style()->columnRuleEquivalent(oldStyle)) {
        // Column rules are painted by anonymous column set children of the
        // multicol container. We need to notify them.
        flowThread->columnRuleStyleDidChange();
      }
    }
  }
}

void LayoutBlockFlow::updateBlockChildDirtyBitsBeforeLayout(
    bool relayoutChildren,
    LayoutBox& child) {
  if (child.isLayoutMultiColumnSpannerPlaceholder())
    toLayoutMultiColumnSpannerPlaceholder(child)
        .markForLayoutIfObjectInFlowThreadNeedsLayout();
  LayoutBlock::updateBlockChildDirtyBitsBeforeLayout(relayoutChildren, child);
}

void LayoutBlockFlow::updateStaticInlinePositionForChild(
    LayoutBox& child,
    LayoutUnit logicalTop,
    IndentTextOrNot indentText) {
  if (child.style()->isOriginalDisplayInlineType())
    setStaticInlinePositionForChild(
        child, startAlignedOffsetForLine(logicalTop, indentText));
  else
    setStaticInlinePositionForChild(child, startOffsetForContent());
}

void LayoutBlockFlow::setStaticInlinePositionForChild(
    LayoutBox& child,
    LayoutUnit inlinePosition) {
  child.layer()->setStaticInlinePosition(inlinePosition);
}

LayoutInline* LayoutBlockFlow::inlineElementContinuation() const {
  LayoutBoxModelObject* continuation = this->continuation();
  return continuation && continuation->isInline() ? toLayoutInline(continuation)
                                                  : nullptr;
}

void LayoutBlockFlow::addChild(LayoutObject* newChild,
                               LayoutObject* beforeChild) {
  if (LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
    if (beforeChild == flowThread)
      beforeChild = flowThread->firstChild();
    ASSERT(!beforeChild || beforeChild->isDescendantOf(flowThread));
    flowThread->addChild(newChild, beforeChild);
    return;
  }

  if (beforeChild && beforeChild->parent() != this) {
    addChildBeforeDescendant(newChild, beforeChild);
    return;
  }

  bool madeBoxesNonInline = false;

  // A block has to either have all of its children inline, or all of its
  // children as blocks.
  // So, if our children are currently inline and a block child has to be
  // inserted, we move all our inline children into anonymous block boxes.
  bool childIsBlockLevel =
      !newChild->isInline() && !newChild->isFloatingOrOutOfFlowPositioned();
  if (childrenInline()) {
    if (childIsBlockLevel) {
      // Wrap the inline content in anonymous blocks, to allow for the new block
      // child to be inserted.
      makeChildrenNonInline(beforeChild);
      madeBoxesNonInline = true;

      if (beforeChild && beforeChild->parent() != this) {
        beforeChild = beforeChild->parent();
        ASSERT(beforeChild->isAnonymousBlock());
        ASSERT(beforeChild->parent() == this);
      }
    }
  } else if (!childIsBlockLevel) {
    // This block has block children. We may want to put the new child into an
    // anomyous block. Floats and out-of-flow children may live among either
    // block or inline children, so for such children, only put them inside an
    // anonymous block if one already exists. If the child is inline, on the
    // other hand, we *have to* put it inside an anonymous block, so create a
    // new one if there is none for us there already.
    LayoutObject* afterChild =
        beforeChild ? beforeChild->previousSibling() : lastChild();

    if (afterChild && afterChild->isAnonymousBlock()) {
      afterChild->addChild(newChild);
      return;
    }

    if (newChild->isInline()) {
      // No suitable existing anonymous box - create a new one.
      LayoutBlockFlow* newBlock = toLayoutBlockFlow(createAnonymousBlock());
      LayoutBox::addChild(newBlock, beforeChild);
      // Reparent adjacent floating or out-of-flow siblings to the new box.
      newBlock->reparentPrecedingFloatingOrOutOfFlowSiblings();
      newBlock->addChild(newChild);
      newBlock->reparentSubsequentFloatingOrOutOfFlowSiblings();
      return;
    }
  }

  // Skip the LayoutBlock override, since that one deals with anonymous child
  // insertion in a way that isn't sufficient for us, and can only cause trouble
  // at this point.
  LayoutBox::addChild(newChild, beforeChild);

  if (madeBoxesNonInline && parent() && isAnonymousBlock() &&
      parent()->isLayoutBlock() && !parent()->createsAnonymousWrapper()) {
    toLayoutBlock(parent())->removeLeftoverAnonymousBlock(this);
    // |this| may be dead now.
  }
}

static bool isMergeableAnonymousBlock(const LayoutBlockFlow* block) {
  return block->isAnonymousBlock() && !block->continuation() &&
         !block->beingDestroyed() && !block->isRubyRun() &&
         !block->isRubyBase();
}

void LayoutBlockFlow::removeChild(LayoutObject* oldChild) {
  // No need to waste time in merging or removing empty anonymous blocks.
  // We can just bail out if our document is getting destroyed.
  if (documentBeingDestroyed()) {
    LayoutBox::removeChild(oldChild);
    return;
  }

  // If this child is a block, and if our previous and next siblings are
  // both anonymous blocks with inline content, then we can go ahead and
  // fold the inline content back together.
  LayoutObject* prev = oldChild->previousSibling();
  LayoutObject* next = oldChild->nextSibling();
  bool mergedAnonymousBlocks = false;
  if (prev && next && !oldChild->isInline() &&
      !oldChild->virtualContinuation() && prev->isLayoutBlockFlow() &&
      next->isLayoutBlockFlow()) {
    if (toLayoutBlockFlow(prev)->mergeSiblingContiguousAnonymousBlock(
            toLayoutBlockFlow(next))) {
      mergedAnonymousBlocks = true;
      next = nullptr;
    }
  }

  LayoutBlock::removeChild(oldChild);

  LayoutObject* child = prev ? prev : next;
  if (child && child->isLayoutBlockFlow() && !child->previousSibling() &&
      !child->nextSibling()) {
    // If the removal has knocked us down to containing only a single anonymous
    // box we can go ahead and pull the content right back up into our
    // box.
    if (mergedAnonymousBlocks ||
        isMergeableAnonymousBlock(toLayoutBlockFlow(child)))
      collapseAnonymousBlockChild(toLayoutBlockFlow(child));
  }

  if (!firstChild()) {
    // If this was our last child be sure to clear out our line boxes.
    if (childrenInline())
      deleteLineBoxTree();

    // If we are an empty anonymous block in the continuation chain,
    // we need to remove ourself and fix the continuation chain.
    if (!beingDestroyed() && isAnonymousBlockContinuation() &&
        !oldChild->isListMarker()) {
      LayoutObject* containingBlockIgnoringAnonymous = containingBlock();
      while (containingBlockIgnoringAnonymous &&
             containingBlockIgnoringAnonymous->isAnonymous())
        containingBlockIgnoringAnonymous =
            containingBlockIgnoringAnonymous->containingBlock();
      for (LayoutObject* curr = this; curr;
           curr = curr->previousInPreOrder(containingBlockIgnoringAnonymous)) {
        if (curr->virtualContinuation() != this)
          continue;

        // Found our previous continuation. We just need to point it to
        // |this|'s next continuation.
        LayoutBoxModelObject* nextContinuation = continuation();
        if (curr->isLayoutInline())
          toLayoutInline(curr)->setContinuation(nextContinuation);
        else if (curr->isLayoutBlockFlow())
          toLayoutBlockFlow(curr)->setContinuation(nextContinuation);
        else
          ASSERT_NOT_REACHED();

        break;
      }
      setContinuation(nullptr);
      destroy();
    }
  } else if (!beingDestroyed() &&
             !oldChild->isFloatingOrOutOfFlowPositioned() &&
             !oldChild->isAnonymousBlock()) {
    // If the child we're removing means that we can now treat all children as
    // inline without the need for anonymous blocks, then do that.
    makeChildrenInlineIfPossible();
  }
}

void LayoutBlockFlow::moveAllChildrenIncludingFloatsTo(LayoutBlock* toBlock,
                                                       bool fullRemoveInsert) {
  LayoutBlockFlow* toBlockFlow = toLayoutBlockFlow(toBlock);
  moveAllChildrenTo(toBlockFlow, fullRemoveInsert);

  // When a portion of the layout tree is being detached, anonymous blocks
  // will be combined as their children are deleted. In this process, the
  // anonymous block later in the tree is merged into the one preceding it.
  // It can happen that the later block (this) contains floats that the
  // previous block (toBlockFlow) did not contain, and thus are not in the
  // floating objects list for toBlockFlow. This can result in toBlockFlow
  // containing floats that are not in it's floating objects list, but are in
  // the floating objects lists of siblings and parents. This can cause problems
  // when the float itself is deleted, since the deletion code assumes that if a
  // float is not in it's containing block's floating objects list, it isn't in
  // any floating objects list. In order to preserve this condition (removing it
  // has serious performance implications), we need to copy the floating objects
  // from the old block (this) to the new block (toBlockFlow).
  // The float's metrics will likely all be wrong, but since toBlockFlow is
  // already marked for layout, this will get fixed before anything gets
  // displayed.
  // See bug https://code.google.com/p/chromium/issues/detail?id=230907
  if (m_floatingObjects) {
    if (!toBlockFlow->m_floatingObjects)
      toBlockFlow->createFloatingObjects();

    const FloatingObjectSet& fromFloatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = fromFloatingObjectSet.end();

    for (FloatingObjectSetIterator it = fromFloatingObjectSet.begin();
         it != end; ++it) {
      const FloatingObject& floatingObject = *it->get();

      // Don't insert the object again if it's already in the list
      if (toBlockFlow->containsFloat(floatingObject.layoutObject()))
        continue;

      toBlockFlow->m_floatingObjects->add(floatingObject.unsafeClone());
    }
  }
}

void LayoutBlockFlow::childBecameFloatingOrOutOfFlow(LayoutBox* child) {
  makeChildrenInlineIfPossible();

  // Reparent the child to an adjacent anonymous block if one is available.
  LayoutObject* prev = child->previousSibling();
  if (prev && prev->isAnonymousBlock() && prev->isLayoutBlockFlow()) {
    LayoutBlockFlow* newContainer = toLayoutBlockFlow(prev);
    moveChildTo(newContainer, child, nullptr, false);
    // The anonymous block we've moved to may now be adjacent to former siblings
    // of ours that it can contain also.
    newContainer->reparentSubsequentFloatingOrOutOfFlowSiblings();
    return;
  }
  LayoutObject* next = child->nextSibling();
  if (next && next->isAnonymousBlock() && next->isLayoutBlockFlow()) {
    LayoutBlockFlow* newContainer = toLayoutBlockFlow(next);
    moveChildTo(newContainer, child, newContainer->firstChild(), false);
  }
}

void LayoutBlockFlow::collapseAnonymousBlockChild(LayoutBlockFlow* child) {
  // It's possible that this block's destruction may have been triggered by the
  // child's removal. Just bail if the anonymous child block is already being
  // destroyed. See crbug.com/282088
  if (child->beingDestroyed())
    return;
  if (child->continuation())
    return;
  // Ruby elements use anonymous wrappers for ruby runs and ruby bases by
  // design, so we don't remove them.
  if (child->isRubyRun() || child->isRubyBase())
    return;
  setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(
      LayoutInvalidationReason::ChildAnonymousBlockChanged);

  child->moveAllChildrenTo(this, child->nextSibling(), child->hasLayer());
  setChildrenInline(child->childrenInline());

  children()->removeChildNode(this, child, child->hasLayer());
  child->destroy();
}

bool LayoutBlockFlow::mergeSiblingContiguousAnonymousBlock(
    LayoutBlockFlow* siblingThatMayBeDeleted) {
  // Note: |this| and |siblingThatMayBeDeleted| may not be adjacent siblings at
  // this point. There may be an object between them which is about to be
  // removed.

  if (!isMergeableAnonymousBlock(this) ||
      !isMergeableAnonymousBlock(siblingThatMayBeDeleted))
    return false;

  setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(
      LayoutInvalidationReason::AnonymousBlockChange);

  // If the inlineness of children of the two block don't match, we'd need
  // special code here (but there should be no need for it).
  ASSERT(siblingThatMayBeDeleted->childrenInline() == childrenInline());
  // Take all the children out of the |next| block and put them in
  // the |prev| block.
  siblingThatMayBeDeleted->moveAllChildrenIncludingFloatsTo(
      this, siblingThatMayBeDeleted->hasLayer() || hasLayer());
  // Delete the now-empty block's lines and nuke it.
  siblingThatMayBeDeleted->deleteLineBoxTree();
  siblingThatMayBeDeleted->destroy();
  return true;
}

void LayoutBlockFlow::reparentSubsequentFloatingOrOutOfFlowSiblings() {
  if (!parent() || !parent()->isLayoutBlockFlow())
    return;
  if (beingDestroyed() || documentBeingDestroyed())
    return;
  LayoutBlockFlow* parentBlockFlow = toLayoutBlockFlow(parent());
  LayoutObject* child = nextSibling();
  while (child && child->isFloatingOrOutOfFlowPositioned()) {
    LayoutObject* sibling = child->nextSibling();
    parentBlockFlow->moveChildTo(this, child, nullptr, false);
    child = sibling;
  }

  if (LayoutObject* next = nextSibling()) {
    if (next->isLayoutBlockFlow())
      mergeSiblingContiguousAnonymousBlock(toLayoutBlockFlow(next));
  }
}

void LayoutBlockFlow::reparentPrecedingFloatingOrOutOfFlowSiblings() {
  if (!parent() || !parent()->isLayoutBlockFlow())
    return;
  if (beingDestroyed() || documentBeingDestroyed())
    return;
  LayoutBlockFlow* parentBlockFlow = toLayoutBlockFlow(parent());
  LayoutObject* child = previousSibling();
  while (child && child->isFloatingOrOutOfFlowPositioned()) {
    LayoutObject* sibling = child->previousSibling();
    parentBlockFlow->moveChildTo(this, child, firstChild(), false);
    child = sibling;
  }
}

void LayoutBlockFlow::makeChildrenInlineIfPossible() {
  // Collapsing away anonymous wrappers isn't relevant for the children of
  // anonymous blocks, unless they are ruby bases.
  if (isAnonymousBlock() && !isRubyBase())
    return;

  Vector<LayoutBlockFlow*, 3> blocksToRemove;
  for (LayoutObject* child = firstChild(); child;
       child = child->nextSibling()) {
    if (child->isFloating())
      continue;
    if (child->isOutOfFlowPositioned())
      continue;

    // There are still block children in the container, so any anonymous
    // wrappers are still needed.
    if (!child->isAnonymousBlock() || !child->isLayoutBlockFlow())
      return;
    // If one of the children is being destroyed then it is unsafe to clean up
    // anonymous wrappers as the
    // entire branch may be being destroyed.
    if (toLayoutBlockFlow(child)->beingDestroyed())
      return;
    // We can't remove anonymous wrappers if they contain continuations as this
    // means there are block children present.
    if (toLayoutBlockFlow(child)->continuation())
      return;
    // We are only interested in removing anonymous wrappers if there are inline
    // siblings underneath them.
    if (!child->childrenInline())
      return;
    // Ruby elements use anonymous wrappers for ruby runs and ruby bases by
    // design, so we don't remove them.
    if (child->isRubyRun() || child->isRubyBase())
      return;

    blocksToRemove.append(toLayoutBlockFlow(child));
  }

  // If we make an object's children inline we are going to frustrate any future
  // attempts to remove floats from its children's float-lists before the next
  // layout happens so clear down all the floatlists now - they will be rebuilt
  // at layout.
  removeFloatingObjectsFromDescendants();

  for (size_t i = 0; i < blocksToRemove.size(); i++)
    collapseAnonymousBlockChild(blocksToRemove[i]);
  setChildrenInline(true);
}

static void getInlineRun(LayoutObject* start,
                         LayoutObject* boundary,
                         LayoutObject*& inlineRunStart,
                         LayoutObject*& inlineRunEnd) {
  // Beginning at |start| we find the largest contiguous run of inlines that
  // we can.  We denote the run with start and end points, |inlineRunStart|
  // and |inlineRunEnd|.  Note that these two values may be the same if
  // we encounter only one inline.
  //
  // We skip any non-inlines we encounter as long as we haven't found any
  // inlines yet.
  //
  // |boundary| indicates a non-inclusive boundary point.  Regardless of whether
  // |boundary| is inline or not, we will not include it in a run with inlines
  // before it. It's as though we encountered a non-inline.

  // Start by skipping as many non-inlines as we can.
  LayoutObject* curr = start;
  bool sawInline;
  do {
    while (curr &&
           !(curr->isInline() || curr->isFloatingOrOutOfFlowPositioned()))
      curr = curr->nextSibling();

    inlineRunStart = inlineRunEnd = curr;

    if (!curr)
      return;  // No more inline children to be found.

    sawInline = curr->isInline();

    curr = curr->nextSibling();
    while (curr &&
           (curr->isInline() || curr->isFloatingOrOutOfFlowPositioned()) &&
           (curr != boundary)) {
      inlineRunEnd = curr;
      if (curr->isInline())
        sawInline = true;
      curr = curr->nextSibling();
    }
  } while (!sawInline);
}

void LayoutBlockFlow::makeChildrenNonInline(LayoutObject* insertionPoint) {
  // makeChildrenNonInline takes a block whose children are *all* inline and it
  // makes sure that inline children are coalesced under anonymous blocks.
  // If |insertionPoint| is defined, then it represents the insertion point for
  // the new block child that is causing us to have to wrap all the inlines.
  // This means that we cannot coalesce inlines before |insertionPoint| with
  // inlines following |insertionPoint|, because the new child is going to be
  // inserted in between the inlines, splitting them.
  ASSERT(!isInline() || isAtomicInlineLevel());
  ASSERT(!insertionPoint || insertionPoint->parent() == this);

  setChildrenInline(false);

  LayoutObject* child = firstChild();
  if (!child)
    return;

  deleteLineBoxTree();

  while (child) {
    LayoutObject* inlineRunStart;
    LayoutObject* inlineRunEnd;
    getInlineRun(child, insertionPoint, inlineRunStart, inlineRunEnd);

    if (!inlineRunStart)
      break;

    child = inlineRunEnd->nextSibling();

    LayoutBlock* block = createAnonymousBlock();
    children()->insertChildNode(this, block, inlineRunStart);
    moveChildrenTo(block, inlineRunStart, child);
  }

#if ENABLE(ASSERT)
  for (LayoutObject* c = firstChild(); c; c = c->nextSibling())
    ASSERT(!c->isInline());
#endif

  setShouldDoFullPaintInvalidation();
}

void LayoutBlockFlow::childBecameNonInline(LayoutObject*) {
  makeChildrenNonInline();
  if (isAnonymousBlock() && parent() && parent()->isLayoutBlock())
    toLayoutBlock(parent())->removeLeftoverAnonymousBlock(this);
  // |this| may be dead here
}

void LayoutBlockFlow::clearFloats(EClear clear) {
  positionNewFloats();
  // set y position
  LayoutUnit newY;
  switch (clear) {
    case ClearLeft:
      newY = lowestFloatLogicalBottom(FloatingObject::FloatLeft);
      break;
    case ClearRight:
      newY = lowestFloatLogicalBottom(FloatingObject::FloatRight);
      break;
    case ClearBoth:
      newY = lowestFloatLogicalBottom();
    default:
      break;
  }
  if (size().height() < newY)
    setLogicalHeight(newY);
}

bool LayoutBlockFlow::containsFloat(LayoutBox* layoutBox) const {
  return m_floatingObjects &&
         m_floatingObjects->set().contains<FloatingObjectHashTranslator>(
             layoutBox);
}

void LayoutBlockFlow::removeFloatingObjects() {
  if (!m_floatingObjects)
    return;

  markSiblingsWithFloatsForLayout();

  m_floatingObjects->clear();
}

LayoutPoint LayoutBlockFlow::flipFloatForWritingModeForChild(
    const FloatingObject& child,
    const LayoutPoint& point) const {
  if (!style()->isFlippedBlocksWritingMode())
    return point;

  // This is similar to LayoutBox::flipForWritingModeForChild. We have to
  // subtract out our left offsets twice, since it's going to get added back in.
  // We hide this complication here so that the calling code looks normal for
  // the unflipped case.
  return LayoutPoint(point.x() + size().width() -
                         child.layoutObject()->size().width() -
                         2 * xPositionForFloatIncludingMargin(child),
                     point.y());
}

LayoutUnit LayoutBlockFlow::logicalLeftOffsetForPositioningFloat(
    LayoutUnit logicalTop,
    LayoutUnit fixedOffset,
    LayoutUnit* heightRemaining) const {
  LayoutUnit offset = fixedOffset;
  if (m_floatingObjects && m_floatingObjects->hasLeftObjects())
    offset = m_floatingObjects->logicalLeftOffsetForPositioningFloat(
        fixedOffset, logicalTop, heightRemaining);
  return adjustLogicalLeftOffsetForLine(offset, DoNotIndentText);
}

LayoutUnit LayoutBlockFlow::logicalRightOffsetForPositioningFloat(
    LayoutUnit logicalTop,
    LayoutUnit fixedOffset,
    LayoutUnit* heightRemaining) const {
  LayoutUnit offset = fixedOffset;
  if (m_floatingObjects && m_floatingObjects->hasRightObjects())
    offset = m_floatingObjects->logicalRightOffsetForPositioningFloat(
        fixedOffset, logicalTop, heightRemaining);
  return adjustLogicalRightOffsetForLine(offset, DoNotIndentText);
}

LayoutUnit LayoutBlockFlow::adjustLogicalLeftOffsetForLine(
    LayoutUnit offsetFromFloats,
    IndentTextOrNot applyTextIndent) const {
  LayoutUnit left = offsetFromFloats;

  if (applyTextIndent == IndentText && style()->isLeftToRightDirection())
    left += textIndentOffset();

  return left;
}

LayoutUnit LayoutBlockFlow::adjustLogicalRightOffsetForLine(
    LayoutUnit offsetFromFloats,
    IndentTextOrNot applyTextIndent) const {
  LayoutUnit right = offsetFromFloats;

  if (applyTextIndent == IndentText && !style()->isLeftToRightDirection())
    right -= textIndentOffset();

  return right;
}

LayoutPoint LayoutBlockFlow::computeLogicalLocationForFloat(
    const FloatingObject& floatingObject,
    LayoutUnit logicalTopOffset) const {
  LayoutBox* childBox = floatingObject.layoutObject();
  LayoutUnit logicalLeftOffset =
      logicalLeftOffsetForContent();  // Constant part of left offset.
  LayoutUnit logicalRightOffset;      // Constant part of right offset.
  logicalRightOffset = logicalRightOffsetForContent();

  LayoutUnit floatLogicalWidth = std::min(
      logicalWidthForFloat(floatingObject),
      logicalRightOffset - logicalLeftOffset);  // The width we look for.

  LayoutUnit floatLogicalLeft;

  bool insideFlowThread = flowThreadContainingBlock();

  if (childBox->style()->floating() == EFloat::Left) {
    LayoutUnit heightRemainingLeft = LayoutUnit(1);
    LayoutUnit heightRemainingRight = LayoutUnit(1);
    floatLogicalLeft = logicalLeftOffsetForPositioningFloat(
        logicalTopOffset, logicalLeftOffset, &heightRemainingLeft);
    while (logicalRightOffsetForPositioningFloat(
               logicalTopOffset, logicalRightOffset, &heightRemainingRight) -
               floatLogicalLeft <
           floatLogicalWidth) {
      logicalTopOffset +=
          std::min<LayoutUnit>(heightRemainingLeft, heightRemainingRight);
      floatLogicalLeft = logicalLeftOffsetForPositioningFloat(
          logicalTopOffset, logicalLeftOffset, &heightRemainingLeft);
      if (insideFlowThread) {
        // Have to re-evaluate all of our offsets, since they may have changed.
        logicalRightOffset =
            logicalRightOffsetForContent();  // Constant part of right offset.
        logicalLeftOffset =
            logicalLeftOffsetForContent();  // Constant part of left offset.
        floatLogicalWidth = std::min(logicalWidthForFloat(floatingObject),
                                     logicalRightOffset - logicalLeftOffset);
      }
    }
    floatLogicalLeft = std::max(
        logicalLeftOffset - borderAndPaddingLogicalLeft(), floatLogicalLeft);
  } else {
    LayoutUnit heightRemainingLeft = LayoutUnit(1);
    LayoutUnit heightRemainingRight = LayoutUnit(1);
    floatLogicalLeft = logicalRightOffsetForPositioningFloat(
        logicalTopOffset, logicalRightOffset, &heightRemainingRight);
    while (floatLogicalLeft -
               logicalLeftOffsetForPositioningFloat(
                   logicalTopOffset, logicalLeftOffset, &heightRemainingLeft) <
           floatLogicalWidth) {
      logicalTopOffset += std::min(heightRemainingLeft, heightRemainingRight);
      floatLogicalLeft = logicalRightOffsetForPositioningFloat(
          logicalTopOffset, logicalRightOffset, &heightRemainingRight);
      if (insideFlowThread) {
        // Have to re-evaluate all of our offsets, since they may have changed.
        logicalRightOffset =
            logicalRightOffsetForContent();  // Constant part of right offset.
        logicalLeftOffset =
            logicalLeftOffsetForContent();  // Constant part of left offset.
        floatLogicalWidth = std::min(logicalWidthForFloat(floatingObject),
                                     logicalRightOffset - logicalLeftOffset);
      }
    }
    // Use the original width of the float here, since the local variable
    // |floatLogicalWidth| was capped to the available line width. See
    // fast/block/float/clamped-right-float.html.
    floatLogicalLeft -= logicalWidthForFloat(floatingObject);
  }

  return LayoutPoint(floatLogicalLeft, logicalTopOffset);
}

FloatingObject* LayoutBlockFlow::insertFloatingObject(LayoutBox& floatBox) {
  ASSERT(floatBox.isFloating());

  // Create the list of special objects if we don't aleady have one
  if (!m_floatingObjects) {
    createFloatingObjects();
  } else {
    // Don't insert the object again if it's already in the list
    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator it =
        floatingObjectSet.find<FloatingObjectHashTranslator>(&floatBox);
    if (it != floatingObjectSet.end())
      return it->get();
  }

  // Create the special object entry & append it to the list

  std::unique_ptr<FloatingObject> newObj = FloatingObject::create(&floatBox);

  // Our location is irrelevant if we're unsplittable or no pagination is in
  // effect. Just go ahead and lay out the float.
  bool isChildLayoutBlock = floatBox.isLayoutBlock();
  if (isChildLayoutBlock && !floatBox.needsLayout() &&
      view()->layoutState()->pageLogicalHeightChanged())
    floatBox.setChildNeedsLayout(MarkOnlyThis);

  floatBox.layoutIfNeeded();

  setLogicalWidthForFloat(*newObj, logicalWidthForChild(floatBox) +
                                       marginStartForChild(floatBox) +
                                       marginEndForChild(floatBox));

  return m_floatingObjects->add(std::move(newObj));
}

void LayoutBlockFlow::removeFloatingObject(LayoutBox* floatBox) {
  if (m_floatingObjects) {
    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator it =
        floatingObjectSet.find<FloatingObjectHashTranslator>(floatBox);
    if (it != floatingObjectSet.end()) {
      FloatingObject& floatingObject = *it->get();
      if (childrenInline()) {
        LayoutUnit logicalTop = logicalTopForFloat(floatingObject);
        LayoutUnit logicalBottom = logicalBottomForFloat(floatingObject);

        // Fix for https://bugs.webkit.org/show_bug.cgi?id=54995.
        if (logicalBottom < 0 || logicalBottom < logicalTop ||
            logicalTop == LayoutUnit::max()) {
          logicalBottom = LayoutUnit::max();
        } else {
          // Special-case zero- and less-than-zero-height floats: those don't
          // touch the line that they're on, but it still needs to be dirtied.
          // This is accomplished by pretending they have a height of 1.
          logicalBottom = std::max(logicalBottom, logicalTop + 1);
        }
        if (floatingObject.originatingLine()) {
          if (!selfNeedsLayout()) {
            ASSERT(
                floatingObject.originatingLine()->getLineLayoutItem().isEqual(
                    this));
            floatingObject.originatingLine()->markDirty();
          }
#if ENABLE(ASSERT)
          floatingObject.setOriginatingLine(nullptr);
#endif
        }
        markLinesDirtyInBlockRange(LayoutUnit(), logicalBottom);
      }
      m_floatingObjects->remove(&floatingObject);
    }
  }
}

void LayoutBlockFlow::removeFloatingObjectsBelow(FloatingObject* lastFloat,
                                                 int logicalOffset) {
  if (!containsFloats())
    return;

  const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
  FloatingObject* curr = floatingObjectSet.last().get();
  while (curr != lastFloat &&
         (!curr->isPlaced() || logicalTopForFloat(*curr) >= logicalOffset)) {
    m_floatingObjects->remove(curr);
    if (floatingObjectSet.isEmpty())
      break;
    curr = floatingObjectSet.last().get();
  }
}

bool LayoutBlockFlow::positionNewFloats(LineWidth* width) {
  if (!m_floatingObjects)
    return false;

  const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
  if (floatingObjectSet.isEmpty())
    return false;

  // If all floats have already been positioned, then we have no work to do.
  if (floatingObjectSet.last()->isPlaced())
    return false;

  // Move backwards through our floating object list until we find a float that
  // has already been positioned. Then we'll be able to move forward,
  // positioning all of the new floats that need it.
  FloatingObjectSetIterator it = floatingObjectSet.end();
  --it;  // Go to last item.
  FloatingObjectSetIterator begin = floatingObjectSet.begin();
  FloatingObject* lastPlacedFloatingObject = nullptr;
  while (it != begin) {
    --it;
    if ((*it)->isPlaced()) {
      lastPlacedFloatingObject = it->get();
      ++it;
      break;
    }
  }

  LayoutUnit logicalTop = logicalHeight();

  // The float cannot start above the top position of the last positioned float.
  if (lastPlacedFloatingObject)
    logicalTop =
        std::max(logicalTopForFloat(*lastPlacedFloatingObject), logicalTop);

  FloatingObjectSetIterator end = floatingObjectSet.end();
  // Now walk through the set of unpositioned floats and place them.
  for (; it != end; ++it) {
    FloatingObject& floatingObject = *it->get();
    // The containing block is responsible for positioning floats, so if we have
    // floats in our list that come from somewhere else, do not attempt to
    // position them.
    if (floatingObject.layoutObject()->containingBlock() != this)
      continue;

    LayoutBox* childBox = floatingObject.layoutObject();

    // FIXME Investigate if this can be removed. crbug.com/370006
    childBox->setMayNeedPaintInvalidation();

    LayoutUnit childLogicalLeftMargin = style()->isLeftToRightDirection()
                                            ? marginStartForChild(*childBox)
                                            : marginEndForChild(*childBox);
    if (childBox->style()->clear() & ClearLeft)
      logicalTop = std::max(lowestFloatLogicalBottom(FloatingObject::FloatLeft),
                            logicalTop);
    if (childBox->style()->clear() & ClearRight)
      logicalTop = std::max(
          lowestFloatLogicalBottom(FloatingObject::FloatRight), logicalTop);

    bool isPaginated = view()->layoutState()->isPaginated();
    if (isPaginated && !childrenInline()) {
      // Forced breaks are inserted at class A break points. Floats may be
      // affected by a break-after value on the previous in-flow sibling.
      if (LayoutBox* previousInFlowBox = childBox->previousInFlowSiblingBox())
        logicalTop =
            applyForcedBreak(logicalTop, previousInFlowBox->breakAfter());
    }

    LayoutPoint floatLogicalLocation =
        computeLogicalLocationForFloat(floatingObject, logicalTop);

    setLogicalLeftForFloat(floatingObject, floatLogicalLocation.x());

    setLogicalLeftForChild(*childBox,
                           floatLogicalLocation.x() + childLogicalLeftMargin);
    setLogicalTopForChild(
        *childBox, floatLogicalLocation.y() + marginBeforeForChild(*childBox));

    SubtreeLayoutScope layoutScope(*childBox);
    if (isPaginated && !childBox->needsLayout())
      markChildForPaginationRelayoutIfNeeded(*childBox, layoutScope);

    childBox->layoutIfNeeded();

    if (isPaginated) {
      LayoutBlockFlow* childBlockFlow =
          childBox->isLayoutBlockFlow() ? toLayoutBlockFlow(childBox) : nullptr;
      // The first piece of content inside the child may have set a strut during
      // layout.
      LayoutUnit strut =
          childBlockFlow ? childBlockFlow->paginationStrutPropagatedFromChild()
                         : LayoutUnit();
      if (!strut) {
        // Otherwise, if we are unsplittable and don't fit, move to the next
        // page or column if that helps the situation.
        strut =
            adjustForUnsplittableChild(*childBox, floatLogicalLocation.y()) -
            floatLogicalLocation.y();
      }

      childBox->setPaginationStrut(strut);
      if (strut) {
        floatLogicalLocation = computeLogicalLocationForFloat(
            floatingObject, floatLogicalLocation.y() + strut);
        setLogicalLeftForFloat(floatingObject, floatLogicalLocation.x());

        setLogicalLeftForChild(
            *childBox, floatLogicalLocation.x() + childLogicalLeftMargin);
        setLogicalTopForChild(*childBox, floatLogicalLocation.y() +
                                             marginBeforeForChild(*childBox));

        if (childBox->isLayoutBlock())
          childBox->setChildNeedsLayout(MarkOnlyThis);
        childBox->layoutIfNeeded();
      }
    }

    setLogicalTopForFloat(floatingObject, floatLogicalLocation.y());

    setLogicalHeightForFloat(floatingObject,
                             logicalHeightForChild(*childBox) +
                                 marginBeforeForChild(*childBox) +
                                 marginAfterForChild(*childBox));

    m_floatingObjects->addPlacedObject(floatingObject);

    if (ShapeOutsideInfo* shapeOutside = childBox->shapeOutsideInfo())
      shapeOutside->setReferenceBoxLogicalSize(logicalSizeForChild(*childBox));

    if (width)
      width->shrinkAvailableWidthForNewFloatIfNeeded(floatingObject);
  }
  return true;
}

bool LayoutBlockFlow::hasOverhangingFloat(LayoutBox* layoutBox) {
  if (!m_floatingObjects || !parent())
    return false;

  const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
  FloatingObjectSetIterator it =
      floatingObjectSet.find<FloatingObjectHashTranslator>(layoutBox);
  if (it == floatingObjectSet.end())
    return false;

  return isOverhangingFloat(**it);
}

void LayoutBlockFlow::addIntrudingFloats(LayoutBlockFlow* prev,
                                         LayoutUnit logicalLeftOffset,
                                         LayoutUnit logicalTopOffset) {
  ASSERT(!avoidsFloats());

  // If we create our own block formatting context then our contents don't
  // interact with floats outside it, even those from our parent.
  if (createsNewFormattingContext())
    return;

  // If the parent or previous sibling doesn't have any floats to add, don't
  // bother.
  if (!prev->m_floatingObjects)
    return;

  logicalLeftOffset += marginLogicalLeft();

  const FloatingObjectSet& prevSet = prev->m_floatingObjects->set();
  FloatingObjectSetIterator prevEnd = prevSet.end();
  for (FloatingObjectSetIterator prevIt = prevSet.begin(); prevIt != prevEnd;
       ++prevIt) {
    FloatingObject& floatingObject = *prevIt->get();
    if (logicalBottomForFloat(floatingObject) > logicalTopOffset) {
      if (!m_floatingObjects ||
          !m_floatingObjects->set().contains(&floatingObject)) {
        // We create the floating object list lazily.
        if (!m_floatingObjects)
          createFloatingObjects();

        // Applying the child's margin makes no sense in the case where the
        // child was passed in since this margin was added already through the
        // modification of the |logicalLeftOffset| variable above.
        // |logicalLeftOffset| will equal the margin in this case, so it's
        // already been taken into account. Only apply this code if prev is the
        // parent, since otherwise the left margin will get applied twice.
        LayoutSize offset =
            isHorizontalWritingMode()
                ? LayoutSize(
                      logicalLeftOffset - (prev != parent() ? prev->marginLeft()
                                                            : LayoutUnit()),
                      logicalTopOffset)
                : LayoutSize(
                      logicalTopOffset,
                      logicalLeftOffset - (prev != parent() ? prev->marginTop()
                                                            : LayoutUnit()));

        m_floatingObjects->add(floatingObject.copyToNewContainer(offset));
      }
    }
  }
}

void LayoutBlockFlow::addOverhangingFloats(LayoutBlockFlow* child,
                                           bool makeChildPaintOtherFloats) {
  // Prevent floats from being added to the canvas by the root element, e.g.,
  // <html>.
  if (!child->containsFloats() || child->createsNewFormattingContext())
    return;

  LayoutUnit childLogicalTop = child->logicalTop();
  LayoutUnit childLogicalLeft = child->logicalLeft();

  // Floats that will remain the child's responsibility to paint should factor
  // into its overflow.
  FloatingObjectSetIterator childEnd = child->m_floatingObjects->set().end();
  for (FloatingObjectSetIterator childIt =
           child->m_floatingObjects->set().begin();
       childIt != childEnd; ++childIt) {
    FloatingObject& floatingObject = *childIt->get();
    LayoutUnit logicalBottomForFloat =
        std::min(this->logicalBottomForFloat(floatingObject),
                 LayoutUnit::max() - childLogicalTop);
    LayoutUnit logicalBottom = childLogicalTop + logicalBottomForFloat;

    if (logicalBottom > logicalHeight()) {
      // If the object is not in the list, we add it now.
      if (!containsFloat(floatingObject.layoutObject())) {
        LayoutSize offset =
            isHorizontalWritingMode()
                ? LayoutSize(-childLogicalLeft, -childLogicalTop)
                : LayoutSize(-childLogicalTop, -childLogicalLeft);
        bool shouldPaint = false;

        // The nearest enclosing layer always paints the float (so that zindex
        // and stacking behaves properly). We always want to propagate the
        // desire to paint the float as far out as we can, to the outermost
        // block that overlaps the float, stopping only if we hit a
        // self-painting layer boundary.
        if (floatingObject.layoutObject()->enclosingFloatPaintingLayer() ==
                enclosingFloatPaintingLayer() &&
            !floatingObject.isLowestNonOverhangingFloatInChild()) {
          floatingObject.setShouldPaint(false);
          shouldPaint = true;
        }
        // We create the floating object list lazily.
        if (!m_floatingObjects)
          createFloatingObjects();

        m_floatingObjects->add(
            floatingObject.copyToNewContainer(offset, shouldPaint, true));
      }
    } else {
      if (makeChildPaintOtherFloats && !floatingObject.shouldPaint() &&
          !floatingObject.layoutObject()->hasSelfPaintingLayer() &&
          !floatingObject.isLowestNonOverhangingFloatInChild() &&
          floatingObject.layoutObject()->isDescendantOf(child) &&
          floatingObject.layoutObject()->enclosingFloatPaintingLayer() ==
              child->enclosingFloatPaintingLayer()) {
        // The float is not overhanging from this block, so if it is a
        // descendant of the child, the child should paint it (the other case is
        // that it is intruding into the child), unless it has its own layer or
        // enclosing layer.
        // If makeChildPaintOtherFloats is false, it means that the child must
        // already know about all the floats it should paint.
        floatingObject.setShouldPaint(true);
      }

      // Since the float doesn't overhang, it didn't get put into our list. We
      // need to go ahead and add its overflow in to the child now.
      if (floatingObject.isDescendant())
        child->addOverflowFromChild(
            floatingObject.layoutObject(),
            LayoutSize(xPositionForFloatIncludingMargin(floatingObject),
                       yPositionForFloatIncludingMargin(floatingObject)));
    }
  }
}

LayoutUnit LayoutBlockFlow::lowestFloatLogicalBottom(
    FloatingObject::Type floatType) const {
  if (!m_floatingObjects)
    return LayoutUnit();

  return m_floatingObjects->lowestFloatLogicalBottom(floatType);
}

LayoutUnit LayoutBlockFlow::nextFloatLogicalBottomBelow(
    LayoutUnit logicalHeight) const {
  if (!m_floatingObjects)
    return logicalHeight;
  return m_floatingObjects->findNextFloatLogicalBottomBelow(logicalHeight);
}

LayoutUnit LayoutBlockFlow::nextFloatLogicalBottomBelowForBlock(
    LayoutUnit logicalHeight) const {
  if (!m_floatingObjects)
    return logicalHeight;

  return m_floatingObjects->findNextFloatLogicalBottomBelowForBlock(
      logicalHeight);
}

Node* LayoutBlockFlow::nodeForHitTest() const {
  // If we are in the margins of block elements that are part of a
  // continuation we're actually still inside the enclosing element
  // that was split. Use the appropriate inner node.
  return isAnonymousBlockContinuation() ? continuation()->node() : node();
}

bool LayoutBlockFlow::hitTestChildren(
    HitTestResult& result,
    const HitTestLocation& locationInContainer,
    const LayoutPoint& accumulatedOffset,
    HitTestAction hitTestAction) {
  LayoutPoint scrolledOffset(hasOverflowClip()
                                 ? accumulatedOffset - scrolledContentOffset()
                                 : accumulatedOffset);

  if (hitTestAction == HitTestFloat &&
      hitTestFloats(result, locationInContainer, scrolledOffset))
    return true;

  if (childrenInline()) {
    if (m_lineBoxes.hitTest(LineLayoutBoxModel(this), result,
                            locationInContainer, scrolledOffset,
                            hitTestAction)) {
      updateHitTestResult(
          result, flipForWritingMode(toLayoutPoint(locationInContainer.point() -
                                                   accumulatedOffset)));
      return true;
    }
  } else if (LayoutBlock::hitTestChildren(result, locationInContainer,
                                          accumulatedOffset, hitTestAction)) {
    return true;
  }

  return false;
}

bool LayoutBlockFlow::hitTestFloats(HitTestResult& result,
                                    const HitTestLocation& locationInContainer,
                                    const LayoutPoint& accumulatedOffset) {
  if (!m_floatingObjects)
    return false;

  LayoutPoint adjustedLocation = accumulatedOffset;
  if (isLayoutView()) {
    DoublePoint position =
        toLayoutView(this)->frameView()->scrollPositionDouble();
    adjustedLocation.move(position.x(), position.y());
  }

  const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
  FloatingObjectSetIterator begin = floatingObjectSet.begin();
  for (FloatingObjectSetIterator it = floatingObjectSet.end(); it != begin;) {
    --it;
    const FloatingObject& floatingObject = *it->get();
    if (floatingObject.shouldPaint()) {
      LayoutUnit xOffset = xPositionForFloatIncludingMargin(floatingObject) -
                           floatingObject.layoutObject()->location().x();
      LayoutUnit yOffset = yPositionForFloatIncludingMargin(floatingObject) -
                           floatingObject.layoutObject()->location().y();
      LayoutPoint childPoint = flipFloatForWritingModeForChild(
          floatingObject, adjustedLocation + LayoutSize(xOffset, yOffset));
      if (floatingObject.layoutObject()->hitTest(result, locationInContainer,
                                                 childPoint)) {
        updateHitTestResult(
            result, locationInContainer.point() - toLayoutSize(childPoint));
        return true;
      }
    }
  }

  return false;
}

LayoutSize LayoutBlockFlow::accumulateInFlowPositionOffsets() const {
  if (!isAnonymousBlock() || !isInFlowPositioned())
    return LayoutSize();
  LayoutSize offset;
  for (const LayoutObject* p = inlineElementContinuation();
       p && p->isLayoutInline(); p = p->parent()) {
    if (p->isInFlowPositioned())
      offset += toLayoutInline(p)->offsetForInFlowPosition();
  }
  return offset;
}

LayoutUnit LayoutBlockFlow::logicalLeftFloatOffsetForLine(
    LayoutUnit logicalTop,
    LayoutUnit fixedOffset,
    LayoutUnit logicalHeight) const {
  if (m_floatingObjects && m_floatingObjects->hasLeftObjects())
    return m_floatingObjects->logicalLeftOffset(fixedOffset, logicalTop,
                                                logicalHeight);

  return fixedOffset;
}

LayoutUnit LayoutBlockFlow::logicalRightFloatOffsetForLine(
    LayoutUnit logicalTop,
    LayoutUnit fixedOffset,
    LayoutUnit logicalHeight) const {
  if (m_floatingObjects && m_floatingObjects->hasRightObjects())
    return m_floatingObjects->logicalRightOffset(fixedOffset, logicalTop,
                                                 logicalHeight);

  return fixedOffset;
}

void LayoutBlockFlow::setAncestorShouldPaintFloatingObject(
    const LayoutBox& floatBox) {
  ASSERT(floatBox.isFloating());
  bool floatBoxIsSelfPaintingLayer =
      floatBox.hasLayer() && floatBox.layer()->isSelfPaintingLayer();
  for (LayoutObject* ancestor = floatBox.parent();
       ancestor && ancestor->isLayoutBlockFlow();
       ancestor = ancestor->parent()) {
    LayoutBlockFlow* ancestorBlock = toLayoutBlockFlow(ancestor);
    FloatingObjects* ancestorFloatingObjects =
        ancestorBlock->m_floatingObjects.get();
    if (!ancestorFloatingObjects)
      break;
    FloatingObjectSet::iterator it = ancestorFloatingObjects->mutableSet()
                                         .find<FloatingObjectHashTranslator>(
                                             const_cast<LayoutBox*>(&floatBox));
    if (it == ancestorFloatingObjects->mutableSet().end())
      break;

    FloatingObject& floatingObject = **it;
    if (!floatBoxIsSelfPaintingLayer) {
      // This repeats the logic in addOverhangingFloats() about shouldPaint
      // flag:
      // - The nearest enclosing block in which the float doesn't overhang
      //   paints the float;
      // - Or even if the float overhangs, if the ancestor block has
      //   self-painting layer, it paints the float.
      if (ancestorBlock->hasSelfPaintingLayer() ||
          !ancestorBlock->isOverhangingFloat(floatingObject)) {
        floatingObject.setShouldPaint(true);
        return;
      }
    } else {
      floatingObject.setShouldPaint(false);
    }
  }
}

bool LayoutBlockFlow::allowsPaginationStrut() const {
  // The block needs to be contained by a LayoutBlockFlow (and not by e.g. a
  // flexbox, grid, or a table (the latter being the case for table cell or
  // table caption)). The reason for this limitation is simply that
  // LayoutBlockFlow child layout code is the only place where we pick up the
  // struts and handle them. We handle floats and regular in-flow children, and
  // that's all. We could handle this in other layout modes as well (and even
  // for out-of-flow children), but currently we don't.
  // TODO(mstensho): But we *should*.
  if (isOutOfFlowPositioned())
    return false;
  if (isLayoutFlowThread()) {
    // Don't let the strut escape the fragmentation context and get lost.
    // TODO(mstensho): If we're in a nested fragmentation context, we should
    // ideally convert and propagate the strut to the outer fragmentation
    // context, so that the inner one is fully pushed to the next outer
    // fragmentainer, instead of taking up unusable space in the previous one.
    // But currently we have no mechanism in place to handle this.
    return false;
  }
  LayoutBlock* containingBlock = this->containingBlock();
  return containingBlock && containingBlock->isLayoutBlockFlow();
}

void LayoutBlockFlow::setPaginationStrutPropagatedFromChild(LayoutUnit strut) {
  strut = std::max(strut, LayoutUnit());
  if (!m_rareData) {
    if (!strut)
      return;
    m_rareData = wrapUnique(new LayoutBlockFlowRareData(this));
  }
  m_rareData->m_paginationStrutPropagatedFromChild = strut;
}

void LayoutBlockFlow::positionSpannerDescendant(
    LayoutMultiColumnSpannerPlaceholder& child) {
  LayoutBox& spanner = *child.layoutObjectInFlowThread();
  // FIXME: |spanner| is a descendant, but never a direct child, so the names
  // here are bad, if nothing else.
  setLogicalTopForChild(spanner, child.logicalTop());
  determineLogicalLeftPositionForChild(spanner);
}

bool LayoutBlockFlow::avoidsFloats() const {
  // Floats can't intrude into our box if we have a non-auto column count or
  // width.
  // Note: we need to use LayoutBox::avoidsFloats here since
  // LayoutBlock::avoidsFloats is always true.
  return LayoutBox::avoidsFloats() || !style()->hasAutoColumnCount() ||
         !style()->hasAutoColumnWidth();
}

void LayoutBlockFlow::moveChildrenTo(LayoutBoxModelObject* toBoxModelObject,
                                     LayoutObject* startChild,
                                     LayoutObject* endChild,
                                     LayoutObject* beforeChild,
                                     bool fullRemoveInsert) {
  if (childrenInline())
    deleteLineBoxTree();
  LayoutBoxModelObject::moveChildrenTo(toBoxModelObject, startChild, endChild,
                                       beforeChild, fullRemoveInsert);
}

LayoutUnit LayoutBlockFlow::logicalLeftSelectionOffset(
    const LayoutBlock* rootBlock,
    LayoutUnit position) const {
  LayoutUnit logicalLeft = logicalLeftOffsetForLine(position, DoNotIndentText);
  if (logicalLeft == logicalLeftOffsetForContent())
    return LayoutBlock::logicalLeftSelectionOffset(rootBlock, position);

  const LayoutBlock* cb = this;
  while (cb != rootBlock) {
    logicalLeft += cb->logicalLeft();
    cb = cb->containingBlock();
  }
  return logicalLeft;
}

LayoutUnit LayoutBlockFlow::logicalRightSelectionOffset(
    const LayoutBlock* rootBlock,
    LayoutUnit position) const {
  LayoutUnit logicalRight =
      logicalRightOffsetForLine(position, DoNotIndentText);
  if (logicalRight == logicalRightOffsetForContent())
    return LayoutBlock::logicalRightSelectionOffset(rootBlock, position);

  const LayoutBlock* cb = this;
  while (cb != rootBlock) {
    logicalRight += cb->logicalLeft();
    cb = cb->containingBlock();
  }
  return logicalRight;
}

RootInlineBox* LayoutBlockFlow::createRootInlineBox() {
  return new RootInlineBox(LineLayoutItem(this));
}

bool LayoutBlockFlow::isPagedOverflow(const ComputedStyle& style) {
  return style.isOverflowPaged() &&
         node() != document().viewportDefiningElement();
}

LayoutBlockFlow::FlowThreadType LayoutBlockFlow::getFlowThreadType(
    const ComputedStyle& style) {
  if (isPagedOverflow(style))
    return PagedFlowThread;
  if (style.specifiesColumns())
    return MultiColumnFlowThread;
  return NoFlowThread;
}

LayoutMultiColumnFlowThread* LayoutBlockFlow::createMultiColumnFlowThread(
    FlowThreadType type) {
  switch (type) {
    case MultiColumnFlowThread:
      return LayoutMultiColumnFlowThread::createAnonymous(document(),
                                                          styleRef());
    case PagedFlowThread:
      // Paged overflow is currently done using the multicol implementation.
      return LayoutPagedFlowThread::createAnonymous(document(), styleRef());
    default:
      ASSERT_NOT_REACHED();
      return nullptr;
  }
}

void LayoutBlockFlow::createOrDestroyMultiColumnFlowThreadIfNeeded(
    const ComputedStyle* oldStyle) {
  // Paged overflow trumps multicol in this implementation. Ideally, it should
  // be possible to have both paged overflow and multicol on the same element,
  // but then we need two flow threads. Anyway, this is nothing to worry about
  // until we can actually nest multicol properly inside other fragmentation
  // contexts.
  FlowThreadType type = getFlowThreadType(styleRef());

  if (multiColumnFlowThread()) {
    ASSERT(oldStyle);
    if (type != getFlowThreadType(*oldStyle)) {
      // If we're no longer to be multicol/paged, destroy the flow thread. Also
      // destroy it when switching between multicol and paged, since that
      // affects the column set structure (multicol containers may have
      // spanners, paged containers may not).
      multiColumnFlowThread()->evacuateAndDestroy();
      ASSERT(!multiColumnFlowThread());
    }
  }

  if (type == NoFlowThread || multiColumnFlowThread())
    return;

  // Ruby elements manage child insertion in a special way, and would mess up
  // insertion of the flow thread. The flow thread needs to be a direct child of
  // the multicol block (|this|).
  if (isRuby())
    return;

  // Form controls are replaced content, and are therefore not supposed to
  // support multicol.
  if (isFileUploadControl() || isTextControl() || isListBox())
    return;

  LayoutMultiColumnFlowThread* flowThread = createMultiColumnFlowThread(type);
  addChild(flowThread);

  // Check that addChild() put the flow thread as a direct child, and didn't do
  // fancy things.
  ASSERT(flowThread->parent() == this);

  flowThread->populate();
  LayoutBlockFlowRareData& rareData = ensureRareData();
  ASSERT(!rareData.m_multiColumnFlowThread);
  rareData.m_multiColumnFlowThread = flowThread;
}

LayoutBlockFlow::LayoutBlockFlowRareData& LayoutBlockFlow::ensureRareData() {
  if (m_rareData)
    return *m_rareData;

  m_rareData = wrapUnique(new LayoutBlockFlowRareData(this));
  return *m_rareData;
}

void LayoutBlockFlow::positionDialog() {
  HTMLDialogElement* dialog = toHTMLDialogElement(node());
  if (dialog->getCenteringMode() == HTMLDialogElement::NotCentered)
    return;

  bool canCenterDialog = (style()->position() == AbsolutePosition ||
                          style()->position() == FixedPosition) &&
                         style()->hasAutoTopAndBottom();

  if (dialog->getCenteringMode() == HTMLDialogElement::Centered) {
    if (canCenterDialog)
      setY(dialog->centeredPosition());
    return;
  }

  ASSERT(dialog->getCenteringMode() == HTMLDialogElement::NeedsCentering);
  if (!canCenterDialog) {
    dialog->setNotCentered();
    return;
  }

  FrameView* frameView = document().view();
  LayoutUnit top = LayoutUnit((style()->position() == FixedPosition)
                                  ? 0
                                  : frameView->scrollOffset().height());
  int visibleHeight = frameView->visibleContentRect(IncludeScrollbars).height();
  if (size().height() < visibleHeight)
    top += (visibleHeight - size().height()) / 2;
  setY(top);
  dialog->setCentered(top);
}

void LayoutBlockFlow::simplifiedNormalFlowInlineLayout() {
  ASSERT(childrenInline());
  ListHashSet<RootInlineBox*> lineBoxes;
  for (InlineWalker walker(LineLayoutBlockFlow(this)); !walker.atEnd();
       walker.advance()) {
    LayoutObject* o = walker.current().layoutObject();
    if (!o->isOutOfFlowPositioned() &&
        (o->isAtomicInlineLevel() || o->isFloating())) {
      o->layoutIfNeeded();
      if (toLayoutBox(o)->inlineBoxWrapper()) {
        RootInlineBox& box = toLayoutBox(o)->inlineBoxWrapper()->root();
        lineBoxes.add(&box);
      }
    } else if (o->isText() ||
               (o->isLayoutInline() && !walker.atEndOfInline())) {
      o->clearNeedsLayout();
    }
  }

  // FIXME: Glyph overflow will get lost in this case, but not really a big
  // deal.
  GlyphOverflowAndFallbackFontsMap textBoxDataMap;
  for (ListHashSet<RootInlineBox*>::const_iterator it = lineBoxes.begin();
       it != lineBoxes.end(); ++it) {
    RootInlineBox* box = *it;
    box->computeOverflow(box->lineTop(), box->lineBottom(), textBoxDataMap);
  }
}

bool LayoutBlockFlow::recalcInlineChildrenOverflowAfterStyleChange() {
  ASSERT(childrenInline());
  bool childrenOverflowChanged = false;
  ListHashSet<RootInlineBox*> lineBoxes;
  for (InlineWalker walker(LineLayoutBlockFlow(this)); !walker.atEnd();
       walker.advance()) {
    LayoutObject* layoutObject = walker.current().layoutObject();
    if (recalcNormalFlowChildOverflowIfNeeded(layoutObject)) {
      childrenOverflowChanged = true;
      if (InlineBox* inlineBoxWrapper =
              toLayoutBlock(layoutObject)->inlineBoxWrapper())
        lineBoxes.add(&inlineBoxWrapper->root());
    }
  }

  // FIXME: Glyph overflow will get lost in this case, but not really a big
  // deal.
  GlyphOverflowAndFallbackFontsMap textBoxDataMap;
  for (ListHashSet<RootInlineBox*>::const_iterator it = lineBoxes.begin();
       it != lineBoxes.end(); ++it) {
    RootInlineBox* box = *it;
    box->clearKnownToHaveNoOverflow();
    box->computeOverflow(box->lineTop(), box->lineBottom(), textBoxDataMap);
  }
  return childrenOverflowChanged;
}

PositionWithAffinity LayoutBlockFlow::positionForPoint(
    const LayoutPoint& point) {
  if (isAtomicInlineLevel()) {
    PositionWithAffinity position =
        positionForPointIfOutsideAtomicInlineLevel(point);
    if (!position.isNull())
      return position;
  }
  if (!childrenInline())
    return LayoutBlock::positionForPoint(point);

  LayoutPoint pointInContents = point;
  offsetForContents(pointInContents);
  LayoutPoint pointInLogicalContents(pointInContents);
  if (!isHorizontalWritingMode())
    pointInLogicalContents = pointInLogicalContents.transposedPoint();

  if (!firstRootBox())
    return createPositionWithAffinity(0);

  bool linesAreFlipped = style()->isFlippedLinesWritingMode();
  bool blocksAreFlipped = style()->isFlippedBlocksWritingMode();

  // look for the closest line box in the root box which is at the passed-in y
  // coordinate
  InlineBox* closestBox = nullptr;
  RootInlineBox* firstRootBoxWithChildren = nullptr;
  RootInlineBox* lastRootBoxWithChildren = nullptr;
  for (RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox()) {
    if (!root->firstLeafChild())
      continue;
    if (!firstRootBoxWithChildren)
      firstRootBoxWithChildren = root;

    if (!linesAreFlipped && root->isFirstAfterPageBreak() &&
        (pointInLogicalContents.y() < root->lineTopWithLeading() ||
         (blocksAreFlipped &&
          pointInLogicalContents.y() == root->lineTopWithLeading())))
      break;

    lastRootBoxWithChildren = root;

    // check if this root line box is located at this y coordinate
    if (pointInLogicalContents.y() < root->selectionBottom() ||
        (blocksAreFlipped &&
         pointInLogicalContents.y() == root->selectionBottom())) {
      if (linesAreFlipped) {
        RootInlineBox* nextRootBoxWithChildren = root->nextRootBox();
        while (nextRootBoxWithChildren &&
               !nextRootBoxWithChildren->firstLeafChild())
          nextRootBoxWithChildren = nextRootBoxWithChildren->nextRootBox();

        if (nextRootBoxWithChildren &&
            nextRootBoxWithChildren->isFirstAfterPageBreak() &&
            (pointInLogicalContents.y() >
                 nextRootBoxWithChildren->lineTopWithLeading() ||
             (!blocksAreFlipped &&
              pointInLogicalContents.y() ==
                  nextRootBoxWithChildren->lineTopWithLeading())))
          continue;
      }
      closestBox = root->closestLeafChildForLogicalLeftPosition(
          pointInLogicalContents.x());
      if (closestBox)
        break;
    }
  }

  bool moveCaretToBoundary =
      document()
          .frame()
          ->editor()
          .behavior()
          .shouldMoveCaretToHorizontalBoundaryWhenPastTopOrBottom();

  if (!moveCaretToBoundary && !closestBox && lastRootBoxWithChildren) {
    // y coordinate is below last root line box, pretend we hit it
    closestBox =
        lastRootBoxWithChildren->closestLeafChildForLogicalLeftPosition(
            pointInLogicalContents.x());
  }

  if (closestBox) {
    if (moveCaretToBoundary) {
      LayoutUnit firstRootBoxWithChildrenTop =
          std::min<LayoutUnit>(firstRootBoxWithChildren->selectionTop(),
                               firstRootBoxWithChildren->logicalTop());
      if (pointInLogicalContents.y() < firstRootBoxWithChildrenTop ||
          (blocksAreFlipped &&
           pointInLogicalContents.y() == firstRootBoxWithChildrenTop)) {
        InlineBox* box = firstRootBoxWithChildren->firstLeafChild();
        if (box->isLineBreak()) {
          if (InlineBox* newBox = box->nextLeafChildIgnoringLineBreak())
            box = newBox;
        }
        // y coordinate is above first root line box, so return the start of the
        // first
        return PositionWithAffinity(positionForBox(box, true));
      }
    }

    // pass the box a top position that is inside it
    LayoutPoint point(pointInLogicalContents.x(),
                      closestBox->root().blockDirectionPointInLine());
    if (!isHorizontalWritingMode())
      point = point.transposedPoint();
    if (closestBox->getLineLayoutItem().isAtomicInlineLevel())
      return positionForPointRespectingEditingBoundaries(
          LineLayoutBox(closestBox->getLineLayoutItem()), point);
    return closestBox->getLineLayoutItem().positionForPoint(point);
  }

  if (lastRootBoxWithChildren) {
    // We hit this case for Mac behavior when the Y coordinate is below the last
    // box.
    ASSERT(moveCaretToBoundary);
    InlineBox* logicallyLastBox;
    if (lastRootBoxWithChildren->getLogicalEndBoxWithNode(logicallyLastBox))
      return PositionWithAffinity(positionForBox(logicallyLastBox, false));
  }

  // Can't reach this. We have a root line box, but it has no kids.
  // FIXME: This should ASSERT_NOT_REACHED(), but clicking on placeholder text
  // seems to hit this code path.
  return createPositionWithAffinity(0);
}

#ifndef NDEBUG

void LayoutBlockFlow::showLineTreeAndMark(const InlineBox* markedBox1,
                                          const char* markedLabel1,
                                          const InlineBox* markedBox2,
                                          const char* markedLabel2,
                                          const LayoutObject* obj) const {
  showLayoutObject();
  for (const RootInlineBox* root = firstRootBox(); root;
       root = root->nextRootBox())
    root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2,
                              markedLabel2, obj, 1);
}

#endif

void LayoutBlockFlow::addOutlineRects(
    Vector<LayoutRect>& rects,
    const LayoutPoint& additionalOffset,
    IncludeBlockVisualOverflowOrNot includeBlockOverflows) const {
  // For blocks inside inlines, we go ahead and include margins so that we run
  // right up to the inline boxes above and below us (thus getting merged with
  // them to form a single irregular shape).
  const LayoutInline* inlineElementContinuation =
      this->inlineElementContinuation();
  if (inlineElementContinuation) {
    // FIXME: This check really isn't accurate.
    bool nextInlineHasLineBox = inlineElementContinuation->firstLineBox();
    // FIXME: This is wrong. The principal layoutObject may not be the
    // continuation preceding this block.
    // FIXME: This is wrong for vertical writing-modes.
    // https://bugs.webkit.org/show_bug.cgi?id=46781
    bool prevInlineHasLineBox =
        toLayoutInline(inlineElementContinuation->node()->layoutObject())
            ->firstLineBox();
    LayoutUnit topMargin =
        prevInlineHasLineBox ? collapsedMarginBefore() : LayoutUnit();
    LayoutUnit bottomMargin =
        nextInlineHasLineBox ? collapsedMarginAfter() : LayoutUnit();
    if (topMargin || bottomMargin) {
      LayoutRect rect(additionalOffset, size());
      rect.expandEdges(topMargin, LayoutUnit(), bottomMargin, LayoutUnit());
      rects.append(rect);
    }
  }

  LayoutBlock::addOutlineRects(rects, additionalOffset, includeBlockOverflows);

  if (includeBlockOverflows == IncludeBlockVisualOverflow &&
      !hasOverflowClip() && !hasControlClip()) {
    for (RootInlineBox* curr = firstRootBox(); curr;
         curr = curr->nextRootBox()) {
      LayoutUnit top = std::max<LayoutUnit>(curr->lineTop(), curr->top());
      LayoutUnit bottom = std::min<LayoutUnit>(curr->lineBottom(),
                                               curr->top() + curr->height());
      LayoutRect rect(additionalOffset.x() + curr->x(),
                      additionalOffset.y() + top, curr->width(), bottom - top);
      if (!rect.isEmpty())
        rects.append(rect);
    }
  }

  if (inlineElementContinuation)
    inlineElementContinuation->addOutlineRects(
        rects, additionalOffset +
                   (inlineElementContinuation->containingBlock()->location() -
                    location()),
        includeBlockOverflows);
}

PaintInvalidationReason LayoutBlockFlow::invalidatePaintIfNeeded(
    const PaintInvalidationState& paintInvalidationState) {
  if (containsFloats())
    paintInvalidationState.paintingLayer().setNeedsPaintPhaseFloat();

  return LayoutBlock::invalidatePaintIfNeeded(paintInvalidationState);
}

void LayoutBlockFlow::invalidateDisplayItemClients(
    PaintInvalidationReason invalidationReason) const {
  BlockFlowPaintInvalidator(*this).invalidateDisplayItemClients(
      invalidationReason);
}

}  // namespace blink