Add the OnAddTrack callback for Objective-C wrapper.

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

Index: webrtc/sdk/objc/Framework/Classes/RTCPeerConnection+Private.h
diff --git a/webrtc/sdk/objc/Framework/Classes/RTCPeerConnection+Private.h b/webrtc/sdk/objc/Framework/Classes/RTCPeerConnection+Private.h
index 60ab868a7c515a9dec6a54f7a4eafe008826cb29..179dd43fe68004dbcb1774659651185ed9e4c0fb 100644
--- a/webrtc/sdk/objc/Framework/Classes/RTCPeerConnection+Private.h
+++ b/webrtc/sdk/objc/Framework/Classes/RTCPeerConnection+Private.h
@@ -49,8 +49,12 @@ class PeerConnectionDelegateAdapter : public PeerConnectionObserver {
   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