Replace GetDoubleValue with ComputeNumber for CSSColorMixValue
Bug: 40946458
Change-Id: If3b40844792d21e0fded85f4a69fbeefc4d0515a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5584818
Commit-Queue: Daniil Sakhapov sakhapov@chromium.org
Reviewed-by: Anders Hartvoll Ruud andruud@chromium.org
Cr-Commit-Position: refs/heads/main@{#1309259}