Bug 1705619 [wpt PR 28532] - [GridNG] Out of flow items with the parent of the grid...

Bug 1705619 [wpt PR 28532] - [GridNG] Out of flow items with the parent of the grid as a containing block, a=testonly

Automatic update from web-platform-tests
[GridNG] Out of flow items with the parent of the grid as a containing
block

This change fixes a test failure where the parent of the grid is the
containing block of an absolutely positioned child of the grid.
Previously, the containing block of out of flow children of the grid was
assumed to be the grid container. As a result, their static position of
was incorrect. Furthermore, this CL fixes the crash when adding a
position fixed item as child of the grid.

Bug: 1045599, 1190220
Change-Id: Iadb035783937bec117d594bb371ac989b08d9d1b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2803842
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Kurt Catti-Schmidt <kschmi@microsoft.com>
Reviewed-by: Ethan Jimenez <ethavar@microsoft.com>
Commit-Queue: Ana Sollano Kim <ansollan@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#876434}

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wpt-commits: 70644c41aaa771c9918606b5df11529dbdfe69c0
wpt-pr: 28532