Restoring behavior where PeerConnection tracks changes to MediaStreams.

talk/app/webrtc/peerconnection.h

Index: talk/app/webrtc/peerconnection.h
diff --git a/talk/app/webrtc/peerconnection.h b/talk/app/webrtc/peerconnection.h
index 25880203500296b1b781c0b76c8113edc6f23fff..be024c5590eafd4508c67a44a07a37cd7a2f5497 100644
--- a/talk/app/webrtc/peerconnection.h
+++ b/talk/app/webrtc/peerconnection.h
@@ -42,6 +42,7 @@
 
 namespace webrtc {
 
+class MediaStreamObserver;
 class RemoteMediaStreamFactory;
 
 typedef std::vector<PortAllocatorFactoryInterface::StunConfiguration>
@@ -217,6 +218,16 @@ class PeerConnection : public PeerConnectionInterface,
   void OnSessionStateChange(WebRtcSession* session, WebRtcSession::State state);
   void ChangeSignalingState(SignalingState signaling_state);
 
+  // Signals from MediaStreamObserver.
+  void OnAudioTrackAdded(AudioTrackInterface* track,
+                         MediaStreamInterface* stream);
+  void OnAudioTrackRemoved(AudioTrackInterface* track,
+                           MediaStreamInterface* stream);
+  void OnVideoTrackAdded(VideoTrackInterface* track,
+                         MediaStreamInterface* stream);
+  void OnVideoTrackRemoved(VideoTrackInterface* track,
+                           MediaStreamInterface* stream);
+
   rtc::Thread* signaling_thread() const {
     return factory_->signaling_thread();
   }
@@ -379,6 +390,8 @@ class PeerConnection : public PeerConnectionInterface,
   // Streams created as a result of SetRemoteDescription.
   rtc::scoped_refptr<StreamCollection> remote_streams_;
 
+  std::vector<rtc::scoped_ptr<MediaStreamObserver>> stream_observers_;
+
   // These lists store track info seen in local/remote descriptions.
   TrackInfos remote_audio_tracks_;
   TrackInfos remote_video_tracks_;