Bug 1678730 [wpt PR 26598] - Force border color at used value time, a=testonly

Bug 1678730 [wpt PR 26598] - Force border color at used value time, a=testonly

Automatic update from web-platform-tests
Force border color at used value time

Forced colors should now happen at used value time. This change adds
an internal property to store the forced colors value of
border-color. This internal value is then applied to the visited
/unvisited border-bottom-color, border-top-color, border-right-color
and border-left-color at used value time when appropriate.

The other forced color properties will be moved in follow up changes.

Bug: 970285
Change-Id: If2da52205595edf38b5009adaedcb0008c87d0e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2511858
Commit-Queue: Alison Maher <almaher@microsoft.com>
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Kevin Ellis <kevers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829899}

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wpt-commits: 8ec588c7fe71ffab79a942c81f84fcb8f7655019
wpt-pr: 26598