Move collapseAnonymousBlockChild() to LayoutBlockFlow, and make it non-static.

Some cleanup in collapseLoneAnonymousBlockChild(). Specify a parent rather than
working it out on our own. Both callers have the parent readily available
anyway.

Remove canCollapseAnonymousBlockChild(), since nobody calls it anymore.

BUG=302024

Review-Url: https://codereview.chromium.org/1980473002
Cr-Commit-Position: refs/heads/master@{#393542}
9 files changed