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* I give up using mock time because it still doesn't drive
  begin frame correctly.
* Factor out the TestReporter as a ThroughputReporterTesterBase template.
* Changed animation_throughput_reporter_unittest to use it.
Bug: 1157649

Change-Id: I876167808bc6c11872de64bfc9bc6e4263592f1f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2581519Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841281}