Missed a change in the rename from initCustomEvent -> $dom_initCustomEvent.

lib/html/src/Isolates.dart

 // Copyright (c) 2012, 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.
 
 _serialize(var message) {
   return new _JsSerializer().traverse(message);
 }
 
 class _JsSerializer extends _Serializer {
 
@@ skipping 175 matching lines @@
       return _portMap[portId].toSendPort();
     } else {
       return new _RemoteSendPortSync(isolateId, portId);
     }
   }
 }
 
 get _isolateId => ReceivePortSync._isolateId;
 
 void _dispatchEvent(String receiver, var message) {
-  var event = document.$dom_createEvent('CustomEvent');
-  event.initCustomEvent(receiver, false, false, JSON.stringify(message));
+  var event = new CustomEvent(receiver, false, false, JSON.stringify(message));
   window.$dom_dispatchEvent(event);
 }
 
 String _getPortSyncEventData(CustomEvent event) => event.detail;