Added a callback function OnAddTrack to PeerConnectionObserver

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

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 182 matching lines @@
         new JsepIceCandidate(candidate.transport_name(), -1, candidate));
     RTCIceCandidate* ice_candidate = [[RTCIceCandidate alloc]
         initWithNativeCandidate:candidate_wrapper.get()];
     [ice_candidates addObject:ice_candidate];
   }
   RTCPeerConnection* peer_connection = peer_connection_;
   [peer_connection.delegate peerConnection:peer_connection
                     didRemoveIceCandidates:ice_candidates];
 }
 
+void PeerConnectionDelegateAdapter::OnAddTrack(
+        rtc::scoped_refptr<RtpReceiverInterface> receiver,
+        std::vector<rtc::scoped_refptr<MediaStreamInterface>> streams) {
+}
+
 }  // namespace webrtc
 
 
 @implementation RTCPeerConnection {
   NSMutableArray<RTCMediaStream *> *_localStreams;
   std::unique_ptr<webrtc::PeerConnectionDelegateAdapter> _observer;
   rtc::scoped_refptr<webrtc::PeerConnectionInterface> _peerConnection;
   BOOL _hasStartedRtcEventLog;
 }
 
@@ skipping 370 matching lines @@
     case RTCStatsOutputLevelDebug:
       return webrtc::PeerConnectionInterface::kStatsOutputLevelDebug;
   }
 }
 
 - (rtc::scoped_refptr<webrtc::PeerConnectionInterface>)nativePeerConnection {
   return _peerConnection;
 }
 
 @end