Sync web-platform-tests PR 38981 into mozilla-central (this bug is closed when the sync is complete).

PR: https://github.com/web-platform-tests/wpt/pull/38981
Details from upstream follow.

Mason Freed <masonf@chromium.org> wrote:

Collect popover invokers on root instead of document

See this HTML spec PR:

https://github.com/whatwg/html/pull/8993

It points out that it would be better to look within root
rather than document for invokers. Otherwise this use case
will be broken:

\<div>
\<template shadowrootmode=open>
\<button popovertarget=p1>Click\</button>
\<div popover id=p1>Popover 1
\<button popovertarget=p2>Click\</button>
\</div>
\<div popover id=p2>Popover 2 (I'm not detected as a being related to p1)\</div>
\</template>
\</div>

I.e. nested popovers entirely within a shadow tree. This CL
fixes that behavior and adds a test.

Bug: 1307772
Change-Id: I28521ec1008d43994ca738c5673da3b704d7ba9c
Reviewed-on: https://chromium-review.googlesource.com/4335444
WPT-Export-Revision: d37768e87ca0a08dc0e9115668dfc50f1afb1273

CI Results

Ran 9 Firefox configurations based on mozilla-central, and Firefox, Chrome, and Safari on GitHub CI

Total 1 tests and 5 subtests

Status Summary

Firefox

OK : 1
FAIL: 5

Chrome

OK : 1
PASS: 4
FAIL: 1

Safari

OK : 1
FAIL: 5

Links

Gecko CI (Treeherder)
GitHub PR Head
GitHub PR Base

Details

New Tests That Don't Pass

• /html/semantics/popovers/popover-shadow-dom.html [wpt.fyi]
  • Popovers located inside shadow DOM can still be shown: FAIL (Chrome: PASS, Safari: FAIL)
  • anchor references do not cross shadow boundaries: FAIL (Chrome: PASS, Safari: FAIL)
  • anchor references use the flat tree not the DOM tree: FAIL (Chrome: PASS, Safari: FAIL)
  • The popover stack is preserved across shadow-inclusive ancestors: FAIL (Chrome: PASS, Safari: FAIL)
  • Popover ancestor relationships are within a root, not within the document: FAIL (Chrome: FAIL, Safari: FAIL)

https://hg.mozilla.org/mozilla-central/rev/6255681320d8
https://hg.mozilla.org/mozilla-central/rev/c798c8aa5fbc