Add histogram stats for AV sync stream offset:

webrtc/video/vie_sync_module.h

 /*
  *  Copyright (c) 2012 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.
  */
 
 // ViESyncModule is responsible for synchronization audio and video for a given
 // VoE and ViE channel couple.
 
 #ifndef WEBRTC_VIDEO_VIE_SYNC_MODULE_H_
 #define WEBRTC_VIDEO_VIE_SYNC_MODULE_H_
 
 #include <memory>
 
 #include "webrtc/base/criticalsection.h"
 #include "webrtc/modules/include/module.h"
 #include "webrtc/system_wrappers/include/tick_util.h"
 #include "webrtc/video/stream_synchronization.h"
 #include "webrtc/voice_engine/include/voe_video_sync.h"
 
 namespace webrtc {
 
+class Clock;
 class RtpRtcp;
 class VideoCodingModule;
+class VideoFrame;
 class ViEChannel;
 class VoEVideoSync;
 
 class ViESyncModule : public Module {
  public:
   explicit ViESyncModule(VideoCodingModule* vcm);
   ~ViESyncModule();
 
   void ConfigureSync(int voe_channel_id,
                      VoEVideoSync* voe_sync_interface,
                      RtpRtcp* video_rtcp_module,
                      RtpReceiver* video_receiver);
 
   // Implements Module.
   int64_t TimeUntilNextProcess() override;
   void Process() override;
 
+  // Gets the sync offset between the current played out audio frame and the
+  // video |frame|. Returns true on success, false otherwise.
+  bool GetStreamSyncOffsetInMs(const VideoFrame& frame,
+                               int64_t* stream_offset_ms) const;
+
  private:
   rtc::CriticalSection data_cs_;
   VideoCodingModule* const vcm_;
+  Clock* const clock_;
   RtpReceiver* video_receiver_;
   RtpRtcp* video_rtp_rtcp_;
   int voe_channel_id_;
   VoEVideoSync* voe_sync_interface_;
   TickTime last_sync_time_;
   std::unique_ptr<StreamSynchronization> sync_;
   StreamSynchronization::Measurements audio_measurement_;
   StreamSynchronization::Measurements video_measurement_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_VIDEO_VIE_SYNC_MODULE_H_