Use StyleColor for the stop-color property

This changes the ComputedStyle storage for the stop-color property to be
a StyleColor rather than a plain color. This fixes explicit inheritance
for the property ('currentcolor' computes to itself).
It also means we'll properly pick up changes to 'color'.

Bug: 914728
Change-Id: I3c78a3615220b9149d1ea5102a6e5863526a6d51
Reviewed-on: https://chromium-review.googlesource.com/c/1377437
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#616660}
11 files changed