Make RTC work on Firefox (mostly).

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index 3bb3ec27a797671c48c9f6109aa6f4a086238033..0bdc70da859a091e240b79e5a98391f724348127 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -17286,7 +17286,13 @@ class RtcDtmfToneChangeEvent extends Event native "RTCDTMFToneChangeEvent" {
 @Experimental
 class RtcIceCandidate native "RTCIceCandidate" {
   factory RtcIceCandidate(Map dictionary) {
-    return JS('RtcIceCandidate', 'new RTCIceCandidate(#)',
+    // TODO(efortuna): Remove this check if when you can actually construct with
+    // the unprefixed RTCIceCandidate in Firefox (currently both are defined,
+    // but one can't be used as a constructor).
+    var constructorName = JS('', 'window[#]',
+        Device.isFirefox ? '${Device.propertyPrefix}RTCIceCandidate' : 
+        'RTCIceCandidate');
+    return JS('RtcIceCandidate', 'new #(#)', constructorName,
         convertDartToNative_SerializedScriptValue(dictionary));
   }
 
@@ -17346,11 +17352,12 @@ class RtcPeerConnection extends EventTarget native "RTCPeerConnection" {
     // Currently in Firefox some of the RTC elements are defined but throw an
     // error unless the user has specifically enabled them in their
     // about:config. So we have to construct an element to actually test if RTC
-    // is supported at at the given time.
+    // is supported at the given time. 
     try {
-      var c = new RtcPeerConnection({"iceServers": [ {"url":"stun:foo.com"}]});
-      return c is RtcPeerConnection;
-    } catch (_) {}
+      new RtcPeerConnection(
+          {"iceServers": [ {"url":"stun:localhost"}]});
+      return true;
+    } catch (_) { return false;}
     return false;
   }
   Future<RtcSessionDescription> createOffer([Map mediaConstraints]) {
@@ -17633,8 +17640,6 @@ class RtcPeerConnection extends EventTarget native "RTCPeerConnection" {
   Stream<Event> get onSignalingStateChange => signalingStateChangeEvent.forTarget(this);
 
 }
-
-
 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
@@ -17645,7 +17650,14 @@ class RtcPeerConnection extends EventTarget native "RTCPeerConnection" {
 @Experimental
 class RtcSessionDescription native "RTCSessionDescription" {
   factory RtcSessionDescription(Map dictionary) {
-    return JS('RtcSessionDescription', 'new RTCSessionDescription(#)',
+    // TODO(efortuna): Remove this check if when you can actually construct with
+    // the unprefixed RTCIceCandidate in Firefox (currently both are defined,
+    // but one can't be used as a constructor).
+    var constructorName = JS('', 'window[#]',
+        Device.isFirefox ? '${Device.propertyPrefix}RTCSessionDescription' : 
+       'RTCSessionDescription');
+    return JS('RtcSessionDescription', 
+        'new #(#)', constructorName,
         convertDartToNative_SerializedScriptValue(dictionary));
   }