Potential deadlock in VideoSendStreamTest::ProducesStats
Potential deadlock in VideoSendStreamTest::ProducesStats

VideoSendStream::GetStats() should not be called by
RtpRtcpObserver::OnSendRtcp(), as at this stage that thread will still
hold internal send locks.

Use an event and signal the test thread to call GetStats() instead.

BUG=
R=mflodman@webrtc.org, pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/9359004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 60ad5fdadf486ad2d516f1d9baeeed7e0fee67f9

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