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Before this cl, VideoTrackAdapter.FramesReceived was logged for all types of MediaStreamVideoSources including remote video sources and pepper api sources.
The indent of this UMA stat is to track if a video capture device output video frames or not.

BUG= 409624

Review URL: https://codereview.chromium.org/529733002

Cr-Commit-Position: refs/heads/master@{#293460}