[LayoutNG] Simplify determining the inline OOF container.

This went through a couple of simplifying revisions, however this now
simplifies where we calculate if an inline level box can contain
something that is out of flow.

There is also a couple of small fixups left over when I was simplifying
this code.

Bug: 636993
Change-Id: I5b660df11ff26d3a7aaf72fdd087a13be65739cf
Reviewed-on: https://chromium-review.googlesource.com/c/1351262
Commit-Queue: Aleks Totic <atotic@chromium.org>
Reviewed-by: Aleks Totic <atotic@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612359}
6 files changed