GitLab

https://crrev.com/544756 ("Make <foreignObject> a stacking context")
added svg-isolation-foreign-isolation.html which had an incorrect
expectation. ForeignObject should create a stacking context [1] and
everything that creates a stacking context is an 'isolated' group [2],
so foreignObject should isolate. Our implementation is correct for html
content in foreignObject but has a bug for svg content in foreignObject.
This patch creates WPT tests for these two scenarios, and marks the svg
variant as failing.

[1] https://svgwg.org/svg2-draft/single-page.html#render-EstablishingStackingContex
[2] https://drafts.fxtf.org/compositing-2/#csscompositingrules_CSS

Bug: 1102803, 1101002
Change-Id: Ia5baceccab0be09eeec5e4682f16247a2881509b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2284631
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#785765}