Add histogram stats for AV sync stream offset:

webrtc/video/video_receive_stream.cc

Index: webrtc/video/video_receive_stream.cc
diff --git a/webrtc/video/video_receive_stream.cc b/webrtc/video/video_receive_stream.cc
index 32fb3e5cc86bc3c54ab170134df1134406efa58b..4f078153f5ed6b2700063383ea947e138ad169b5 100644
--- a/webrtc/video/video_receive_stream.cc
+++ b/webrtc/video/video_receive_stream.cc
@@ -380,6 +380,10 @@ void VideoReceiveStream::FrameCallback(VideoFrame* video_frame) {
 
 int VideoReceiveStream::RenderFrame(const uint32_t /*stream_id*/,
                                     const VideoFrame& video_frame) {
+  int64_t sync_offset_ms;
+  if (vie_sync_.GetStreamSyncOffsetInMs(video_frame, &sync_offset_ms))
+    stats_proxy_.OnSyncOffsetUpdated(sync_offset_ms);

[stefan-webrtc, 2016/03/09 15:59:30]

Nice, thanks!

I wonder if we instead should expose the current playout time in NTP in
GetStats()? In that case it would be possible for the user to compute the sync
offset to any stream, instead of us choosing what (audio) stream to compare with
here. What do you think? I think that is probably a later improvement either
way, since that would require that we implement that stat for audio too...

[åsapersson, 2016/03/10 09:08:35]

Sounds good. Maybe as a later improvement?

[stefan-webrtc, 2016/03/10 14:25:09]

Yes

+
   // TODO(pbos): Wire up config_.render->IsTextureSupported() and convert if not
   // supported. Or provide methods for converting a texture frame in
   // VideoFrame.