Merge most of LayoutBox::mapLocalToAncestor() into LayoutObject.

Just kept the part that updates the IsFixed MapCoordinatesMode, since it wasn't
intertwined with the rest and is unique to LayoutBox-derived classes.

BUG=568492
R=leviw@chromium.org

Review URL: https://codereview.chromium.org/1700743002

Cr-Commit-Position: refs/heads/master@{#376126}
2 files changed