tree 7c8ad130c72bd53a64e2c0ed36da57756ac6c63a
parent b74014abe0da655dd4675b1ddce4364eabc0b3de
author Alison Maher <almaher@microsoft.com> 1615840723 -0700
committer Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> 1615841880 -0700

[LayoutNG] Nested abspos/fixedpos in multicol

Nested abspos elements in a multicol whose outer abspos started in a
new column was broken. The reason being that the inner abspos was added
as a descendant twice. Once when PropagateOOFPositionedInfo() was called
during OOF layout, and a second time when the new column was added
as a child to the multicol builder via AddChild().

To fix this, add a bool to AddChild() and AddResult() to determine
whether or not we should propagate up OOF descendants. This prevents us
from adding such inner abspos elements as descendants twice, as well as
avoiding repeated OOF descendants when building up the multicol
builder in a nested fragmentation context.

As a part of this change, I also moved the propagation of
non-fragmentainer OOF descendants into PropagateOOFPositionedInfo()
since we can skip such work in the above cases, as well. Previous to
this change, nested fixedpos elements inside a multicol weren't getting
laid out. This fixes the problem for simple multicol scenarios. However,
this does not fix the problem for nested fragmentation contexts or for
cases where the containing block of the fixedpos is somewhere inside the
multicol.

Thus, nested fixedpos handling will likely need to be handled in a
different way. However, I've added a simple wpt test for a nested
fixedpos to illustrate what behavior is currently working.

Bug: 1079031
Change-Id: I6fd5af2249a374676158f491717f8cc03b447e9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2754727
Commit-Queue: Alison Maher <almaher@microsoft.com>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#862929}