fast/media/color-does-not-include-alpha.html passes now

BUG=243593
TBR=jamesr@chromium.org

Review URL: https://codereview.chromium.org/49843004

git-svn-id: svn://svn.chromium.org/blink/trunk@160761 bbb929c8-8fbe-4397-9dbb-9b2b20218538