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 12f8d1bd4b73b993625c8a97ee1e3ad71d25edb0..3423f850a6f7ce5b91a1ffbe02e1f666cdfa4205 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>
@@ -201,6 +202,16 @@ 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();
   }
@@ -364,6 +375,8 @@ 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_;