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- Move two tests for AnimationHost/WorkletAnimation interactions to animation_host_unittests
- Remove unnecessary complexity related to creating and testing an impl instance.
  These tests don't need to distinguish between main/impl instances at all.

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I928e664ddf4fab8496fbbe3a09fcdcd120c875fb
Reviewed-on: https://chromium-review.googlesource.com/1133770Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Majid Valipour <majidvp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578405}