Convert css3/blending/svg-blend-multiply-alpha to a pixel test

1) we're now rendering differently on Mac

2) the ref has hard-coded colors, so there's little/no value over
   a pixel test

BUG=730071
TBR=mtklein@chromium.org,dpranke@chromium.org

Review-Url: https://codereview.chromium.org/2926873002
Cr-Commit-Position: refs/heads/master@{#477712}
2 files changed