Check if fragment's block size fits into a layout opportunity.

Since we started using LayoutOpportunity iterator for positioning BFC
fragments, we can't longer rely on the assumption that
FindLayoutOpportunityForFragment will be used for floats only.

List of changes:
- Change FindLayoutOpportunityForFragment to check if fragment's block
  size fits into a layout opportunity.
- Change NGInlineLayoutAlgorithm to avoid adding font's descent to
  line_bottom if the text only includes object replacement characters
  I need it to fix floats-wrap-top-below-002l-ref.xht.

BUG=635619

Review-Url: https://codereview.chromium.org/2840883002
Cr-Commit-Position: refs/heads/master@{#467875}
4 files changed