[webui] Re-Enable cr-lottie tests

It's not clear if these tests will still be flaky on the CI or not. We
made some changes that may have deflaked them.

Bug: 1103865, 1021474b
Change-Id: Icfe7ed6637868fc29e30c0d182f985a6b38aa000
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2311144


Commit-Queue: Nina Satragno <nsatragno@chromium.org>
Auto-Submit: Nina Satragno <nsatragno@chromium.org>
Reviewed-by: dpapad <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791463}