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This CL adds metrics for the video player, which includes user clicks
on various buttons, video latency, and various video playback states.
Some more metrics will be added in the next CL.

Bug: 1117155
Change-Id: I6ef8a515dfff43c66ca2197cf8db087b058db236
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2434096Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812565}