Adding "first packet received" notification to PeerConnectionObserver.

talk/app/webrtc/java/testcommon/src/org/webrtc/PeerConnectionTest.java

Index: talk/app/webrtc/java/testcommon/src/org/webrtc/PeerConnectionTest.java
diff --git a/talk/app/webrtc/java/testcommon/src/org/webrtc/PeerConnectionTest.java b/talk/app/webrtc/java/testcommon/src/org/webrtc/PeerConnectionTest.java
index 50f4d7317f33a11e146ef18af96d63164f833956..8db0ded9f7e91f7fb41911fbd612c4d621ef0394 100644
--- a/talk/app/webrtc/java/testcommon/src/org/webrtc/PeerConnectionTest.java
+++ b/talk/app/webrtc/java/testcommon/src/org/webrtc/PeerConnectionTest.java
@@ -289,6 +289,9 @@ public class PeerConnectionTest {
       ++expectedStatsCallbacks;
     }
 
+    @Override
+    public synchronized void onFirstMediaPacketReceived() {}
+
     public synchronized LinkedList<StatsReport[]> takeStatsReports() {
       LinkedList<StatsReport[]> got = gotStatsReports;
       gotStatsReports = new LinkedList<StatsReport[]>();