Unbreak build by adding new mandatory ICE username param.

R=wu@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/2182004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@4689 4adac7df-926f-26a2-2b94-8c16560cd09d

talk/app/webrtc/objctests/RTCPeerConnectionTest.mm

@@ -99,6 +99,7 @@
   NSString *stunURL = @"stun:stun.l.google.com:19302";
   RTCICEServer *stunServer =
       [[RTCICEServer alloc] initWithURI:[NSURL URLWithString:stunURL]
+                               username:@""
                                password:@""];
   NSArray *iceServers = @[stunServer];