Change VideoRtpReceiver to create remote VideoTrack and VideoTrackSource.

webrtc/api/videotracksource.h

 /*
  *  Copyright 2016 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.
  */
 
 #ifndef WEBRTC_API_VIDEOTRACKSOURCE_H_
 #define WEBRTC_API_VIDEOTRACKSOURCE_H_
 
 #include "webrtc/api/notifier.h"
 #include "webrtc/api/videosourceinterface.h"
 #include "webrtc/media/base/mediachannel.h"
 #include "webrtc/media/base/videosinkinterface.h"
 
 // VideoTrackSource implements VideoTrackSourceInterface.
 namespace webrtc {
 
 class VideoTrackSource : public Notifier<VideoTrackSourceInterface> {
  public:
   VideoTrackSource(rtc::VideoSourceInterface<cricket::VideoFrame>* source,
                    rtc::Thread* worker_thread,
                    bool remote);
+  void SetState(SourceState new_state);
+  // OnSourceDestroyed clears this instance pointer to |source_|. It is useful
+  // when the underlying rtc::VideoSourceInterface is destroyed before the
+  // reference counted VideoTrackSource.
+  void OnSourceDestroyed();
 
-  void SetState(SourceState new_state);
   SourceState state() const override { return state_; }
   bool remote() const override { return remote_; }
 
   void Stop() override{};
   void Restart() override{};
 
-  virtual bool is_screencast() const { return false; };
-  virtual bool needs_denoising() const { return false; };
+  virtual bool is_screencast() const { return false; }
+  virtual bool needs_denoising() const { return false; }
 
   void AddOrUpdateSink(rtc::VideoSinkInterface<cricket::VideoFrame>* sink,
                        const rtc::VideoSinkWants& wants) override;
   void RemoveSink(rtc::VideoSinkInterface<cricket::VideoFrame>* sink) override;
 
+  cricket::VideoCapturer* GetVideoCapturer() override { return nullptr; }
+
  protected:
   rtc::Thread* worker_thread() { return worker_thread_; }
 
  private:
   rtc::VideoSourceInterface<cricket::VideoFrame>* source_;
   rtc::Thread* worker_thread_;
   cricket::VideoOptions options_;
   SourceState state_;
   const bool remote_;
 };
 
 }  // namespace webrtc
 
 #endif  //  WEBRTC_API_VIDEOTRACKSOURCE_H_