[LayoutNG] Enable inline children special code for flow threads.

PlaceChildrenInLayoutBox() has special code for inline child fragments, to
basically skip them, unless we find floats. This wasn't executed for multicol.
This caused DCHECK failures and incorrect layout.

A few new tests now pass. One regresses, but that's because the test expected a
float to be at block offset 0, which it happened to be, since we didn't even
attempt to place it. Now we place it. We place it incorrectly, but at least we
place it. :)

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: Ifee30438885c267f9d6c271a0db2f5c0f191fad6
Reviewed-on: https://chromium-review.googlesource.com/713858
Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@opera.com>
Cr-Commit-Position: refs/heads/master@{#508126}
3 files changed