Add histogram stats for AV sync stream offset:

webrtc/video/receive_statistics_proxy.h

 /*
  *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 28 matching lines @@
                                public StreamDataCountersCallback {
  public:
   ReceiveStatisticsProxy(const VideoReceiveStream::Config& config,
                          Clock* clock);
   virtual ~ReceiveStatisticsProxy();
 
   VideoReceiveStream::Stats GetStats() const;
 
   void OnDecodedFrame();
   void OnRenderedFrame(const VideoFrame& frame);
+  void OnSyncOffsetUpdated(int64_t sync_offset_ms);
   void OnIncomingPayloadType(int payload_type);
   void OnDecoderImplementationName(const char* implementation_name);
   void OnIncomingRate(unsigned int framerate, unsigned int bitrate_bps);
   void OnDecoderTiming(int decode_ms,
                        int max_decode_ms,
                        int current_delay_ms,
                        int target_delay_ms,
                        int jitter_buffer_ms,
                        int min_playout_delay_ms,
                        int render_delay_ms,
@@ skipping 40 matching lines @@
   const VideoReceiveStream::Config config_;
 
   rtc::CriticalSection crit_;
   VideoReceiveStream::Stats stats_ GUARDED_BY(crit_);
   RateStatistics decode_fps_estimator_ GUARDED_BY(crit_);
   RateStatistics renders_fps_estimator_ GUARDED_BY(crit_);
   rtc::RateTracker render_fps_tracker_ GUARDED_BY(crit_);
   rtc::RateTracker render_pixel_tracker_ GUARDED_BY(crit_);
   SampleCounter render_width_counter_ GUARDED_BY(crit_);
   SampleCounter render_height_counter_ GUARDED_BY(crit_);
+  SampleCounter sync_offset_counter_ GUARDED_BY(crit_);
   SampleCounter decode_time_counter_ GUARDED_BY(crit_);
   SampleCounter delay_counter_ GUARDED_BY(crit_);
   ReportBlockStats report_block_stats_ GUARDED_BY(crit_);
   QpCounters qp_counters_;  // Only accessed on the decoding thread.
   std::map<uint32_t, StreamDataCounters> rtx_stats_ GUARDED_BY(crit_);
 };
 
 }  // namespace webrtc
 #endif  // WEBRTC_VIDEO_RECEIVE_STATISTICS_PROXY_H_