Update READMEs for animation tests
First in a series of patches to document best practices for animation
tests. This patch adds a readme for non-WPT animation tests, and
updates the readme for CSS transitions. Each tip was recently used to
fix a flake / failure introduced with the migration of css transition
tests from using run_web_test.py to run_wpt_test.py.
Change-Id: Iaba7ea397c4f55a090b08a71c046b96c64453bd9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6037955
Reviewed-by: Olga Gerchikov gerchiko@microsoft.com
Commit-Queue: Kevin Ellis kevers@chromium.org
Cr-Commit-Position: refs/heads/main@{#1387067}