Add histogram stats for AV sync stream offset:

webrtc/video/vie_sync_module.h

Index: webrtc/video/vie_sync_module.h
diff --git a/webrtc/video/vie_sync_module.h b/webrtc/video/vie_sync_module.h
index 5724ce799a7307caba2c0c0162b14f1b72affefe..b08dd8a79965b252d0f746dfda67db76eb6ab268 100644
--- a/webrtc/video/vie_sync_module.h
+++ b/webrtc/video/vie_sync_module.h
@@ -23,8 +23,10 @@
 
 namespace webrtc {
 
+class Clock;
 class RtpRtcp;
 class VideoCodingModule;
+class VideoFrame;
 class ViEChannel;
 class VoEVideoSync;
 
@@ -42,9 +44,14 @@ class ViESyncModule : public Module {
   int64_t TimeUntilNextProcess() override;
   void Process() override;
 
+  // Returns the absolute value of the sync offset between the video |frame| and
+  // the current played out audio frame (or -1 on error).

[pbos-webrtc, 2016/03/04 14:34:27]

-1 if not configured/in use?

[åsapersson, 2016/03/09 15:44:35]

Done.

+  int64_t GetStreamSyncOffsetInMs(const VideoFrame& frame);

[stefan-webrtc, 2016/03/04 14:32:17]

Would it be reasonable to request a unittest here too?

[åsapersson, 2016/03/09 15:44:35]

I will look into adding unittest for this class. Maybe in a separate CL?

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

Sure no problem.

+
  private:
   rtc::CriticalSection data_cs_;
   VideoCodingModule* const vcm_;
+  Clock* const clock_;
   RtpReceiver* video_receiver_;
   RtpRtcp* video_rtp_rtcp_;
   int voe_channel_id_;