Bug 1834584 [wpt PR 40169] - CSS parsing of scrollbar-color, a=testonly

Bug 1834584 [wpt PR 40169] - CSS parsing of scrollbar-color, a=testonly

Automatic update from web-platform-tests
CSS parsing of scrollbar-color

The scrollbar-color CSS property allows the author to set the
thumb and track color of an element's scrollbar.
Its syntax is "auto | <color>{2}".

This is behind the ScrollbarColor feature flag (status: experimental)

See the CSS Scrollbars spec for more details:
https://drafts.csswg.org/css-scrollbars

Bug: 891944
Change-Id: I16494e5cb4e412c09a5ee88154b9ead39551ed5f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4557165
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1148657}

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wpt-commits: b22c9bb52f359e46d30f8812d6cc83c2742816e4
wpt-pr: 40169