Use ASCII case conversion in color input validation.

All valid color strings are ASCII.

Bug: 627682
Change-Id: Ib169ff7c1014557ac50286435b443dc1e3104533
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574210
Reviewed-by: Hayato Ito <hayato@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652669}
1 file changed