Change VideoRtpReceiver to create remote VideoTrack and VideoTrackSource.

webrtc/api/videotracksource.cc

 /*
  *  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.
  */
 
@@ skipping 14 matching lines @@
       state_(kInitializing),
       remote_(remote) {}
 
 void VideoTrackSource::SetState(SourceState new_state) {
   if (state_ != new_state) {
     state_ = new_state;
     FireOnChanged();
   }
 }
 
+void VideoTrackSource::OnSourceDestroyed() {
+  source_ = nullptr;
+}
+
 void VideoTrackSource::AddOrUpdateSink(
     rtc::VideoSinkInterface<cricket::VideoFrame>* sink,
     const rtc::VideoSinkWants& wants) {
+  if (!source_) {
+    return;
+  }
   worker_thread_->Invoke<void>(rtc::Bind(
       &rtc::VideoSourceInterface<cricket::VideoFrame>::AddOrUpdateSink, source_,
       sink, wants));
 }
 
 void VideoTrackSource::RemoveSink(
     rtc::VideoSinkInterface<cricket::VideoFrame>* sink) {
+  if (!source_) {
+    return;
+  }
   worker_thread_->Invoke<void>(
       rtc::Bind(&rtc::VideoSourceInterface<cricket::VideoFrame>::RemoveSink,
                 source_, sink));
 }
 
 }  //  namespace webrtc