Added a callback function OnAddTrack to PeerConnectionObserver

webrtc/api/peerconnection.cc

Index: webrtc/api/peerconnection.cc
diff --git a/webrtc/api/peerconnection.cc b/webrtc/api/peerconnection.cc
index 2f320d78edfd93f079bc41de6f53b2f3f13e7d59..0bdc30b7419f00bc1e6553cbb8db76fb190b67fd 100644
--- a/webrtc/api/peerconnection.cc
+++ b/webrtc/api/peerconnection.cc
@@ -1420,20 +1420,29 @@ void PeerConnection::OnMessage(rtc::Message* msg) {
 void PeerConnection::CreateAudioReceiver(MediaStreamInterface* stream,
                                          const std::string& track_id,
                                          uint32_t ssrc) {
-  receivers_.push_back(
-      RtpReceiverProxyWithInternal<RtpReceiverInternal>::Create(
+  rtc::scoped_refptr<RtpReceiverProxyWithInternal<RtpReceiverInternal>>
+      receiver = RtpReceiverProxyWithInternal<RtpReceiverInternal>::Create(
           signaling_thread(), new AudioRtpReceiver(stream, track_id, ssrc,
-                                                   session_->voice_channel())));
+                                                   session_->voice_channel()));
+
+  receivers_.push_back(receiver);
+  std::vector<rtc::scoped_refptr<MediaStreamInterface>> streams;
+  streams.push_back(rtc::scoped_refptr<MediaStreamInterface>(stream));

[honghaiz3, 2016/11/17 01:19:02]

Is there any reason to use a vector of streams here?

[Zhi Huang, 2016/11/17 01:42:06]

According to the spec: https://www.w3.org/TR/webrtc/#dom-rtctrackevent
the event has a sequence of MediaStream. I think this means a track can be
attached to multiple streams. We may call this OnAddTrack() function once we
encounter that case.

[Taylor Brandstetter, 2016/11/17 02:07:25]

I agree about this. Even if we take a long time to support multiple streams for
one track (or never support it), we might as well be forward thinking so we
don't need to change the callback later.

+  observer_->OnAddTrack(receiver, streams);

[honghaiz3, 2016/11/17 01:52:31]

Should we just get the track from the receiver and use that as the argument?
Something like observer_->OnAddTrack(receiver->track(), stream)?

 }
 
 void PeerConnection::CreateVideoReceiver(MediaStreamInterface* stream,
                                          const std::string& track_id,
                                          uint32_t ssrc) {
-  receivers_.push_back(
-      RtpReceiverProxyWithInternal<RtpReceiverInternal>::Create(
+  rtc::scoped_refptr<RtpReceiverProxyWithInternal<RtpReceiverInternal>>
+      receiver = RtpReceiverProxyWithInternal<RtpReceiverInternal>::Create(
           signaling_thread(),
           new VideoRtpReceiver(stream, track_id, factory_->worker_thread(),
-                               ssrc, session_->video_channel())));
+                               ssrc, session_->video_channel()));
+  receivers_.push_back(receiver);
+  std::vector<rtc::scoped_refptr<MediaStreamInterface>> streams;
+  streams.push_back(rtc::scoped_refptr<MediaStreamInterface>(stream));
+  observer_->OnAddTrack(receiver, streams);
 }
 
 // TODO(deadbeef): Keep RtpReceivers around even if track goes away in remote