Make RTC work on Firefox (mostly).

tools/dom/templates/html/dart2js/impl_RTCIceCandidate.darttemplate

Index: tools/dom/templates/html/dart2js/impl_RTCIceCandidate.darttemplate
diff --git a/tools/dom/templates/html/dart2js/impl_RTCIceCandidate.darttemplate b/tools/dom/templates/html/dart2js/impl_RTCIceCandidate.darttemplate
index ce3ebd7b2a99febc428232dc2dd4ad202d1f6783..6090f900702b66235e70ecfa0eca6c84807c4798 100644
--- a/tools/dom/templates/html/dart2js/impl_RTCIceCandidate.darttemplate
+++ b/tools/dom/templates/html/dart2js/impl_RTCIceCandidate.darttemplate
@@ -6,7 +6,13 @@ part of $LIBRARYNAME;
 
 $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   factory $CLASSNAME(Map dictionary) {
-    return JS('RtcIceCandidate', 'new RTCIceCandidate(#)',
+    // TODO(efortuna): Remove this check if when you can actually construct with
+    // the unprefixed RTCIceCandidate in Firefox (currently both are defined,
+    // but one can't be used as a constructor).
+    var constructorName = JS('', 'window[#]',
+        Device.isFirefox ? '${Device.propertyPrefix}RTCIceCandidate' : 
+        'RTCIceCandidate');
+    return JS('RtcIceCandidate', 'new #(#)', constructorName,
         convertDartToNative_SerializedScriptValue(dictionary));
   }
 $!MEMBERS