Add the OnAddTrack callback for Objective-C wrapper.

webrtc/sdk/objc/Framework/Classes/RTCPeerConnection.mm

Index: webrtc/sdk/objc/Framework/Classes/RTCPeerConnection.mm
diff --git a/webrtc/sdk/objc/Framework/Classes/RTCPeerConnection.mm b/webrtc/sdk/objc/Framework/Classes/RTCPeerConnection.mm
index de7608c3b9941dd1acffc6b8e8dc0d5c52211379..25020d88f71af00fe49f20649db6bda4ab459880 100644
--- a/webrtc/sdk/objc/Framework/Classes/RTCPeerConnection.mm
+++ b/webrtc/sdk/objc/Framework/Classes/RTCPeerConnection.mm
@@ -127,9 +127,8 @@ void PeerConnectionDelegateAdapter::OnSignalingChange(
 
 void PeerConnectionDelegateAdapter::OnAddStream(
     rtc::scoped_refptr<MediaStreamInterface> stream) {
-  RTCMediaStream *mediaStream =
-      [[RTCMediaStream alloc] initWithNativeMediaStream:stream];
   RTCPeerConnection *peer_connection = peer_connection_;
+  RTCMediaStream *mediaStream = [peer_connection mediaStreamForNativeStream:stream];
   [peer_connection.delegate peerConnection:peer_connection
                               didAddStream:mediaStream];
 }
@@ -141,6 +140,7 @@ void PeerConnectionDelegateAdapter::OnRemoveStream(
   RTCPeerConnection *peer_connection = peer_connection_;
   [peer_connection.delegate peerConnection:peer_connection
                            didRemoveStream:mediaStream];
+  [peer_connection removeNativeMediaStream:stream];
 }
 
 void PeerConnectionDelegateAdapter::OnDataChannel(
@@ -200,6 +200,25 @@ void PeerConnectionDelegateAdapter::OnIceCandidatesRemoved(
                     didRemoveIceCandidates:ice_candidates];
 }
 
+void PeerConnectionDelegateAdapter::OnAddTrack(
+    rtc::scoped_refptr<RtpReceiverInterface> receiver,
+    const std::vector<rtc::scoped_refptr<MediaStreamInterface>>& streams) {
+  RTCRtpReceiver* rtpReceiver =
+      [[RTCRtpReceiver alloc] initWithNativeRtpReceiver:receiver];
+  NSMutableArray* mediaStreams =
+      [NSMutableArray arrayWithCapacity:streams.size()];
+
+  RTCPeerConnection* peer_connection = peer_connection_;
+  for (const auto stream : streams) {
+    RTCMediaStream* mediaStream =
+        [peer_connection mediaStreamForNativeStream:stream];
+    [mediaStreams addObject:mediaStream];
+  }
+  [peer_connection.delegate peerConnection:peer_connection

[tkchin_webrtc, 2017/02/22 18:13:18]

since you marked it optional, you have to check if the delegate responds to the
selector, otherwise this will cause a crash for old clients

[Zhi Huang, 2017/02/23 05:26:54]

Done.

+                               didAddTrack:rtpReceiver
+                                   streams:mediaStreams];
+}
+
 }  // namespace webrtc
 
 
@@ -209,6 +228,7 @@ void PeerConnectionDelegateAdapter::OnIceCandidatesRemoved(
   rtc::scoped_refptr<webrtc::PeerConnectionInterface> _peerConnection;
   std::unique_ptr<webrtc::MediaConstraints> _nativeConstraints;
   BOOL _hasStartedRtcEventLog;
+  NSMutableDictionary<NSNumber *, RTCMediaStream *> *_mediaStreamsByStreamId;
 }
 
 @synthesize delegate = _delegate;
@@ -238,6 +258,7 @@ void PeerConnectionDelegateAdapter::OnIceCandidatesRemoved(
     }
     _localStreams = [[NSMutableArray alloc] init];
     _delegate = delegate;
+    _mediaStreamsByStreamId = [NSMutableDictionary dictionary];
   }
   return self;
 }
@@ -588,6 +609,23 @@ void PeerConnectionDelegateAdapter::OnIceCandidatesRemoved(
   }
 }
 
+- (RTCMediaStream *)mediaStreamForNativeStream:
+    (rtc::scoped_refptr<webrtc::MediaStreamInterface>)stream {
+  RTCMediaStream *mediaStream =
+      _mediaStreamsByStreamId[[NSNumber numberWithLong:(long)stream.get()]];

[tkchin_webrtc, 2017/02/22 18:13:18]

per Taylor's comment, can we use the ID instead of the pointer value?
also, use @( ), and use a local var for the key instead of creating multiple
NSNumber

[Zhi Huang, 2017/02/23 05:26:54]

Sorry I missed this comment.

I assume Taylor means "label()".
https://cs.chromium.org/chromium/src/third_party/webrtc/api/mediastreaminterf...

[Taylor Brandstetter, 2017/02/23 05:30:05]

Yeah; I forgot, streams have "labels" while tracks have "IDs"

+  if (!mediaStream) {
+    mediaStream =
+        [[RTCMediaStream alloc] initWithNativeMediaStream:stream.get()];
+    _mediaStreamsByStreamId[[NSNumber numberWithLong:(long)stream.get()]] =
+        mediaStream;
+  }
+  return mediaStream;
+}
+
+- (void)removeNativeMediaStream:(rtc::scoped_refptr<webrtc::MediaStreamInterface>)stream {
+  [_mediaStreamsByStreamId removeObjectForKey:[NSNumber numberWithLong:(long)stream.get()]];
+}
+
 - (rtc::scoped_refptr<webrtc::PeerConnectionInterface>)nativePeerConnection {
   return _peerConnection;
 }