Bug 1610547 [wpt PR 21308] - [FlexNG] Use previous constraint space for layout roots...

Bug 1610547 [wpt PR 21308] - [FlexNG] Use previous constraint space for layout roots., a=testonly

Automatic update from web-platform-tests
[FlexNG] Use previous constraint space for layout roots.

Devtools had an issue where elements were sized at 0px height.
This was caused by the relayout boundary logic not working correctly.

In Devtools these elements had layout and size containment triggering
ObjectIsRelayoutBoundary() to return true.

The call to NGConstraintSpace::CreateFromLayoutObject for this flex-item
was incorrect as it wasn't using the stretched size (as we don't
set HasOverrideLogicalWidth(), etc).

This refactors the various callers of
NGConstraintSpace::CreateFromLayoutObject and create a new method
UpdateInFlowBlockLayout which contains the previously (duplicated)
logic.

This new method will try and use the previous constraint space (if
it is a layout root), instead of creating it.

Bug: 845235
Change-Id: I52ddb9d58ae010305b980657bb434a30d5b7fbbb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2010983
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: David Grogan <dgrogan@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734420}

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wpt-commits: fb09ccb613400a3a0327967063cb1117cea96468
wpt-pr: 21308