Bug 1467351 [wpt PR 11374] - [css-contain] Layout containment overflowing contents...

Bug 1467351 [wpt PR 11374] - [css-contain] Layout containment overflowing contents as ink overflow, a=testonly

Automatic update from web-platform-tests[css-contain] Layout containment overflowing contents as ink overflow

Text form the spec
(https://drafts.csswg.org/css-contain/#containment-layout):
  "If the contents of the element overflow the element,
  they must be treated as ink overflow."

The patch modifies LayoutBox::LayoutOverflowRectForPropagation()
so the overflowing contents of an element with "contain: layout"
are treated as ink overflow. That way they don't interfere at all
in the layout of its ancestors.

BUG=843320
TEST=external/wpt/css/css-contain/contain-layout-015.html

Change-Id: Iedd47edf46a0e4ce0e4102abe5881d25771fe0fa
Reviewed-on: https://chromium-review.googlesource.com/1087462
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Manuel Rego Casasnovas <rego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#564826}

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wpt-commits: 892738fabee6bc4c7e720177f45e295fcb981b8d
wpt-pr: 11374