Bug 1663100 [wpt PR 25402] - Restrict attachInternals() to be run ins…

…ide or after the constructor, a=testonly

Automatic update from web-platform-tests
Restrict attachInternals() to be run inside or after the constructor

Per the discussion at [1], the intention of this change is to prevent
calls to attachInternals() prior to the constructor of the custom
element having a chance to do so. The spec PR is at [2].

This change is gated behind the DeclarativeShadowDOM flag. With the
flag disabled (the default), a use counter is added for checking on
the web compatibility of this change. The use counter will measure
the cases where attachInternals() is being called in a to-be-outlawed
way.

[1] WICG/webcomponents#871 (comment)
[2] whatwg/html#5909

Bug: 1042130
Change-Id: Iacf97a49133b5f7f44710e5c0287f01cfebe4c44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2392975
Reviewed-by: Alexei Svitkine <asvitkinechromium.org>
Reviewed-by: Kouhei Ueno <kouheichromium.org>
Commit-Queue: Mason Freed <masonfreedchromium.org>
Auto-Submit: Mason Freed <masonfreedchromium.org>
Cr-Commit-Position: refs/heads/master{#806830}

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wpt-commits: df5b354d012f3bb0db1524bfaf8a4e16b4b01cc2
wpt-pr: 25402

UltraBlame original commit: 56afece076c057fd659c3c180e1673c5a409a614