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We add a trace event when we present the video swapchain. These events
includes presentation mode and pixel format. Based on existence of such
events and their params, we can decide if the expected video frame
presentation happened.

Note that we found out that GetFrameStatisticsMedia is flaky and this is
out of our control. So if a test fails because of this, we repeat it a
couple times.

BUG=867136
TEST=GPU bots
R=kbr@chromium.org,piman@chromium.org,sunnyps@chromium.org

Change-Id: I1f0972f2887a72ad46f533edda274ffc7608790b
Reviewed-on: https://chromium-review.googlesource.com/c/1441374Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Zhenyao Mo <zmo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628563}