Created a java wrapper for the callback OnAddTrack to PeerConnection.Observer

webrtc/examples/androidapp/src/org/appspot/apprtc/PeerConnectionClient.java

Index: webrtc/examples/androidapp/src/org/appspot/apprtc/PeerConnectionClient.java
diff --git a/webrtc/examples/androidapp/src/org/appspot/apprtc/PeerConnectionClient.java b/webrtc/examples/androidapp/src/org/appspot/apprtc/PeerConnectionClient.java
index 61784a0fd385d96f3b74ebd9dd6e12e339c6f546..cc5e457cbf0594e1514371af193517a0169cd09b 100644
--- a/webrtc/examples/androidapp/src/org/appspot/apprtc/PeerConnectionClient.java
+++ b/webrtc/examples/androidapp/src/org/appspot/apprtc/PeerConnectionClient.java
@@ -41,6 +41,7 @@ import org.webrtc.PeerConnection;
 import org.webrtc.PeerConnection.IceConnectionState;
 import org.webrtc.PeerConnectionFactory;
 import org.webrtc.RtpParameters;
+import org.webrtc.RtpReceiver;
 import org.webrtc.RtpSender;
 import org.webrtc.SdpObserver;
 import org.webrtc.SessionDescription;
@@ -1175,6 +1176,9 @@ public class PeerConnectionClient {
       // No need to do anything; AppRTC follows a pre-agreed-upon
       // signaling/negotiation protocol.
     }
+
+    @Override
+    public void onAddTrack(final RtpReceiver receiver, final MediaStream[] mediaStreams) {}
   }
 
   // Implementation detail: handle offer creation/signaling and answer setting,