Make RTC work on Firefox (mostly).

tools/dom/templates/html/impl/impl_RTCPeerConnection.darttemplate

Index: tools/dom/templates/html/impl/impl_RTCPeerConnection.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_RTCPeerConnection.darttemplate b/tools/dom/templates/html/impl/impl_RTCPeerConnection.darttemplate
index 46dcc3775229c547d72f5b2f5a437e4ea6882357..3731099e569ac1f8863030731b2b2309e493aeb9 100644
--- a/tools/dom/templates/html/impl/impl_RTCPeerConnection.darttemplate
+++ b/tools/dom/templates/html/impl/impl_RTCPeerConnection.darttemplate
@@ -29,9 +29,12 @@ $if DART2JS
     // 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 at the given time. Additionally, Firefox only supports IP
+    // numbers (currently), so we test with a random IP address.
+    // See https://bugzilla.mozilla.org/show_bug.cgi?id=837919 for details.
     try {
-      var c = new RtcPeerConnection({"iceServers": [ {"url":"stun:foo.com"}]});
+      var c = new RtcPeerConnection(
+          {"iceServers": [ {"url":"stun:216.93.246.18"}]});
       return c is RtcPeerConnection;
     } catch (_) {}
     return false;
@@ -56,5 +59,3 @@ $endif
   }
 $!MEMBERS
 }
-
-