Bug 1836072 [wpt PR 40324] - Fix scrollbar-width repaint issues on non viewports...

Bug 1836072 [wpt PR 40324] - Fix scrollbar-width repaint issues on non viewports, a=testonly

Automatic update from web-platform-tests
Fix scrollbar-width repaint issues on non viewports

This patch fixes issues with dynamically switching between
scrollbar-width values.

Previously the ScrollbarWidth check would prevent
SetScrollbarNeedsPaintInvalidation from being called.

ScrollbarWidth is still checked for none values inside
ComputeScrollbarExistence and ScrollbarTheme implementations.

Only viewport level changes are still broken.

WPT tests included

Change-Id: I606e3ba7cecca160045af70f42cfea0567370216
Bug: 891944
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4567548
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1155115}

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wpt-commits: a73e0d1ef317d164c58e51cd82006e9684649932
wpt-pr: 40324