GitLab

When we decide to switch over to legacy layout for a block formatting
context (and the entire subtree) because there's something editable, we
used to only set ForceLegacyLayout on those nodes that create layout
objects, but that isn't enough. There may be descendants of box-less
nodes that may create layout objects later on, and, since
ForceLegacyLayout is an inherited "property", we need to set it on all
potential parent nodes. Otherwise we risk inserting NG objects that
participate in a legacy block formatting context, which isn't allowed
[1].

This matters when we have display:contents (which is very common
situation for shadow DOM slot elements, for instance).

Checking with the layout parent's style whether to force legacy layout
or not fixes the problem.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1127027
enforces this.

Bug: 863040
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: I6133c20493017b4648b153f2c7558c76589c3d89
Reviewed-on: https://chromium-review.googlesource.com/1136445Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579360}