These tests are not taking advantage of tools in the web-animations
API. Modernized the implementation of the test and migrated to WPT.
There is no reason these tests need to be pixel tests since we
simply need to determine that the computed style is interpolated
correctly for property values that are missing in the first or last
keyframe.

Bug: 1383194
Change-Id: I600eac2d31b6fc4def12f62518cf7af35225b0b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4103740


Reviewed-by: Mustaq Ahmed <mustaq@chromium.org>
Commit-Queue: Kevin Ellis <kevers@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1083190}