Added a callback function OnAddTrack to PeerConnectionObserver

webrtc/api/test/peerconnectiontestwrapper.h

Index: webrtc/api/test/peerconnectiontestwrapper.h
diff --git a/webrtc/api/test/peerconnectiontestwrapper.h b/webrtc/api/test/peerconnectiontestwrapper.h
index 3cdac492f1910fd297ee7673191f7282d526eb0a..03f9bb384d85b295299ca965dc0bab9d42277691 100644
--- a/webrtc/api/test/peerconnectiontestwrapper.h
+++ b/webrtc/api/test/peerconnectiontestwrapper.h
@@ -65,6 +65,9 @@ class PeerConnectionTestWrapper
       webrtc::PeerConnectionInterface::IceGatheringState new_state) {}
   virtual void OnIceCandidate(const webrtc::IceCandidateInterface* candidate);
   virtual void OnIceComplete() {}
+  virtual void OnAddTrack(
+      rtc::scoped_refptr<webrtc::RtpReceiverInterface> receiver,
+      std::vector<rtc::scoped_refptr<webrtc::MediaStreamInterface>> streams) {}
 
   // Implements CreateSessionDescriptionObserver.
   virtual void OnSuccess(webrtc::SessionDescriptionInterface* desc);