Change VideoRtpReceiver to create remote VideoTrack and VideoTrackSource.

webrtc/media/base/videobroadcaster.h

Index: webrtc/media/base/videobroadcaster.h
diff --git a/webrtc/media/base/videobroadcaster.h b/webrtc/media/base/videobroadcaster.h
index 89c9f3dd49cbfbab58d11c6078c34606306d7ecb..b4227eaba6f314fe65f73492be7ae5d1b43ea4c8 100644
--- a/webrtc/media/base/videobroadcaster.h
+++ b/webrtc/media/base/videobroadcaster.h
@@ -14,6 +14,7 @@
 #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"
@@ -21,6 +22,12 @@
 
 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:
@@ -46,13 +53,15 @@ class VideoBroadcaster : public VideoSourceInterface<cricket::VideoFrame>,
     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