Adding "first packet received" notification to PeerConnectionObserver.

talk/app/webrtc/objc/RTCPeerConnectionObserver.mm

Index: talk/app/webrtc/objc/RTCPeerConnectionObserver.mm
diff --git a/talk/app/webrtc/objc/RTCPeerConnectionObserver.mm b/talk/app/webrtc/objc/RTCPeerConnectionObserver.mm
index 411cd6cb899a9a9ba33041884ff33a49b3a3c8c0..47246cbef7040c0e46b2fdcf1c60f598d018bc22 100644
--- a/talk/app/webrtc/objc/RTCPeerConnectionObserver.mm
+++ b/talk/app/webrtc/objc/RTCPeerConnectionObserver.mm
@@ -105,4 +105,9 @@ void RTCPeerConnectionObserver::OnIceCandidate(
                            gotICECandidate:iceCandidate];
 }
 
+void RTCPeerConnectionObserver::OnFirstMediaPacketReceived() {
+  id<RTCPeerConnectionDelegate> delegate = _peerConnection.delegate;
+  [delegate peerConnectionOnFirstMediaPacketReceived:_peerConnection];
+}
+
 }  // namespace webrtc