Add traces for some video receive statistics.
Add traces for some video receive statistics.

This CL adds traces to compute the following metrics that getStats()
captures for video:
- googFrameRateOutput
- packetsLost
- googFrameWidthReceived
- googFrameHeightReceived
- googCurrentDelayMs
- googTargetDelayMs
- googDecodeMs
- googMaxDecodeMs
- googJitterBufferMs
- googRenderDelayMs

BUG=chromium:653087

Review-Url: https://codereview.webrtc.org/2884643004
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#18242}

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