Add the OnAddTrack callback for Objective-C wrapper.

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCPeerConnection.h

Index: webrtc/sdk/objc/Framework/Headers/WebRTC/RTCPeerConnection.h
diff --git a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCPeerConnection.h b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCPeerConnection.h
index 4438eb28ab5ecf4fb53c4a7e645ff0c08bd4c5da..ed4aaf0f555fe928e654fcebb8585c2a4bd9c7e5 100644
--- a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCPeerConnection.h
+++ b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCPeerConnection.h
@@ -106,6 +106,12 @@ RTC_EXPORT
 - (void)peerConnection:(RTCPeerConnection *)peerConnection
     didOpenDataChannel:(RTCDataChannel *)dataChannel;
 
+@optional
+/** Called when a new track is signaled from remote peer. */
+- (void)peerConnection:(RTCPeerConnection*)peerConnection
+    didAddTrack:(RTCRtpReceiver*)rtpReceiver

[tkchin_webrtc, 2016/11/22 20:41:34]

align :

space after *
(RTCPeerConnection *)
NSArray<RTCMediaStream *> *)

[Zhi Huang, 2016/11/22 23:38:42]

Done.

Should I align the ":" in previous functions such as
"didChangeIceConnectionState" ?

+    attachedStreams:(NSArray<RTCMediaStream*>*)mediaStreams;

[tkchin_webrtc, 2016/11/22 20:41:34]

Seems different than spec?
https://www.w3.org/TR/webrtc/#dom-rtctrackevent

Would've expected:
- (void)peerConnection:(RTCPeerConnection *)peerConnection
didAddTrack:(RTCMediaStreamTrack *)track
streams:(NSArray<RTCMediaStream *> *)streams
transceiver:(RTCRtpTransceiver *)transceiver;

[Zhi Huang, 2016/11/22 23:38:42]

According to the spec, the Receiver is required. We can easily get the Track
from the Receiver, not the other way around.
We don't have transceivers yet.

I think it would be fine as long as the native api provide enough info for JS
api.

I agree that this may seems a little bit confusing. Maybe make it clear with
comments?

+
 @end
 
 RTC_EXPORT