Get VideoCapturer stats via VideoTrackSourceInterface in StatsCollector,

webrtc/api/rtpsender.h

 /*
  *  Copyright 2015 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 83 matching lines @@
     stream_id_ = stream_id;
   }
   std::string stream_id() const override { return stream_id_; }
 
   void Stop() override;
 
   RtpParameters GetParameters() const;
   bool SetParameters(const RtpParameters& parameters);
 
  private:
+  // TODO(nisse): Since SSRC == 0 is technically valid, figure out
+  // some other way to test if we have a valid SSRC.
   bool can_send_track() const { return track_ && ssrc_; }
   // Helper function to construct options for
   // AudioProviderInterface::SetAudioSend.
   void SetAudioSend();
 
   std::string id_;
   std::string stream_id_;
   AudioProviderInterface* provider_;
   StatsCollector* stats_;
   rtc::scoped_refptr<AudioTrackInterface> track_;
@@ skipping 61 matching lines @@
   VideoProviderInterface* provider_;
   rtc::scoped_refptr<VideoTrackInterface> track_;
   uint32_t ssrc_ = 0;
   bool cached_track_enabled_ = false;
   bool stopped_ = false;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_RTPSENDER_H_