Add the OnAddTrack callback for Objective-C wrapper.

webrtc/sdk/objc/Framework/Classes/RTCPeerConnection+Private.h

 /*
  *  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 31 matching lines @@
       PeerConnectionInterface::IceConnectionState new_state) override;
 
   void OnIceGatheringChange(
       PeerConnectionInterface::IceGatheringState new_state) override;
 
   void OnIceCandidate(const IceCandidateInterface *candidate) override;
 
   void OnIceCandidatesRemoved(
       const std::vector<cricket::Candidate>& candidates) override;
 
+  void OnAddTrack(
+      rtc::scoped_refptr<RtpReceiverInterface> receiver,
+      const std::vector<rtc::scoped_refptr<MediaStreamInterface>>& streams) override;
+
  private:
-  __weak RTCPeerConnection *peer_connection_;
+  __weak RTCPeerConnection* peer_connection_;
 };
 
 } // namespace webrtc
 
 
 @interface RTCPeerConnection ()
 
 /** The native PeerConnectionInterface created during construction. */
 @property(nonatomic, readonly)
     rtc::scoped_refptr<webrtc::PeerConnectionInterface> nativePeerConnection;
@@ skipping 34 matching lines @@
     (webrtc::PeerConnectionInterface::IceGatheringState)nativeState;
 
 + (NSString *)stringForIceGatheringState:(RTCIceGatheringState)state;
 
 + (webrtc::PeerConnectionInterface::StatsOutputLevel)
     nativeStatsOutputLevelForLevel:(RTCStatsOutputLevel)level;
 
 @end
 
 NS_ASSUME_NONNULL_END