Change VideoRtpReceiver to create remote VideoTrack and VideoTrackSource.

webrtc/media/base/videobroadcaster.h

 /*
  *  Copyright (c) 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_MEDIA_BASE_VIDEOBROADCASTER_H_
 #define WEBRTC_MEDIA_BASE_VIDEOBROADCASTER_H_
 
 #include <utility>
 #include <vector>
 
+#include "webrtc/base/criticalsection.h"
 #include "webrtc/base/thread_checker.h"
 #include "webrtc/media/base/videoframe.h"
 #include "webrtc/media/base/videosinkinterface.h"
 #include "webrtc/media/base/videosourceinterface.h"
 
 namespace rtc {
 
+// VideoBroadcaster broadcast video frames to sinks and combines
+// VideoSinkWants from its sinks. It does that by implementing
+// rtc::VideoSourceInterface and rtc::VideoSinkInterface.
+// Sinks must be added and removed on one and only one thread.
+// Video frames can be broadcasted on any thread. I.e VideoBroadcaster::OnFrame
+// can be called on any thread.
 class VideoBroadcaster : public VideoSourceInterface<cricket::VideoFrame>,
                          public VideoSinkInterface<cricket::VideoFrame> {
  public:
   VideoBroadcaster();
   void AddOrUpdateSink(VideoSinkInterface<cricket::VideoFrame>* sink,
                        const VideoSinkWants& wants) override;
   void RemoveSink(VideoSinkInterface<cricket::VideoFrame>* sink) override;
 
   // Returns true if the next frame will be delivered to at least one sink.
   bool frame_wanted() const;
 
   // Returns VideoSinkWants a source is requested to fulfill. They are
   // aggregated by all VideoSinkWants from all sinks.
   VideoSinkWants wants() const;
 
   void OnFrame(const cricket::VideoFrame& frame) override;
 
  protected:
   struct SinkPair {
     SinkPair(VideoSinkInterface<cricket::VideoFrame>* sink,
              VideoSinkWants wants)
         : sink(sink), wants(wants) {}
     VideoSinkInterface<cricket::VideoFrame>* sink;
     VideoSinkWants wants;
   };
-  SinkPair* FindSinkPair(const VideoSinkInterface<cricket::VideoFrame>* sink);
-  void UpdateWants();
+  SinkPair* FindSinkPair(const VideoSinkInterface<cricket::VideoFrame>* sink)
+      EXCLUSIVE_LOCKS_REQUIRED(sinks_and_wants_lock_);
+  void UpdateWants() EXCLUSIVE_LOCKS_REQUIRED(sinks_and_wants_lock_);
 
   ThreadChecker thread_checker_;
+  rtc::CriticalSection sinks_and_wants_lock_;
 
-  VideoSinkWants current_wants_;
-  std::vector<SinkPair> sinks_;
+  VideoSinkWants current_wants_ GUARDED_BY(sinks_and_wants_lock_);
+  std::vector<SinkPair> sinks_ GUARDED_BY(sinks_and_wants_lock_);
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_MEDIA_BASE_VIDEOBROADCASTER_H_