merge_pr_45

Port display interpolation to wpt

Both Chrome and Firefox pass

Bug: 900581
Change-Id: Ic686da5cf98667dd8c2be2e004c7f9b368a5d03d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1940871
Reviewed-by: Xida Chen xidachen@chromium.org
Commit-Queue: Hao Sheng haozhes@chromium.org
Cr-Commit-Position: refs/heads/master@{#719750}