Refactor slow tests in css/css-transitions.
Very wasteful to simply let the animations run given the sheer number
of animations. This batch of tests also liberally uses setTimeout,
which is no longer permitted in WPT tests.
Added a step to catch when all transitions have started, then simply
sample the computed value at fixed values for animation.currentTime.
The animations are left running with currentTime aligned with the
end of the transition, which makes the transitionend events imminent.
Rather than time based, each step in the batch processing is promise
based.
Bug: 375377010,375587482
Change-Id: I8a071a9c5e0c99770d91acb24c8b67a745ace616
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5979045
Reviewed-by: Olga Gerchikov gerchiko@microsoft.com
Commit-Queue: Kevin Ellis kevers@chromium.org
Cr-Commit-Position: refs/heads/main@{#1377078}