Added a callback function OnAddTrack to PeerConnectionObserver

webrtc/examples/peerconnection/client/conductor.h

Index: webrtc/examples/peerconnection/client/conductor.h
diff --git a/webrtc/examples/peerconnection/client/conductor.h b/webrtc/examples/peerconnection/client/conductor.h
index 74e5f6c5a2e56b8f35c30ede06c0e9504bdb05f1..1b8006ac944635ac7bfceeea5ecd3fad0c8fecd8 100644
--- a/webrtc/examples/peerconnection/client/conductor.h
+++ b/webrtc/examples/peerconnection/client/conductor.h
@@ -16,6 +16,7 @@
 #include <map>
 #include <set>
 #include <string>
+#include <vector>
 
 #include "webrtc/api/mediastreaminterface.h"
 #include "webrtc/api/peerconnectioninterface.h"
@@ -79,6 +80,9 @@ class Conductor
       webrtc::PeerConnectionInterface::IceGatheringState new_state) override{};
   void OnIceCandidate(const webrtc::IceCandidateInterface* candidate) override;
   void OnIceConnectionReceivingChange(bool receiving) override {}
+  void OnAddTrack(rtc::scoped_refptr<webrtc::RtpReceiverInterface> receiver,
+                  std::vector<rtc::scoped_refptr<webrtc::MediaStreamInterface>>
+                      streams) override {}
 
   //
   // PeerConnectionClientObserver implementation.