Remove support for attribute event listeners.

client/dom/generated/src/wrapping/_MessagePortWrappingImplementation.dart

 // Copyright (c) 2011, 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.
 
 // WARNING: Do not edit - generated code.
 
 class _MessagePortWrappingImplementation extends DOMWrapperBase implements MessagePort {
   _MessagePortWrappingImplementation() : super() {}
 
   static create__MessagePortWrappingImplementation() native {
     return new _MessagePortWrappingImplementation();
   }
 
-  EventListener get onmessage() { return _get_onmessage(this); }
-  static EventListener _get_onmessage(var _this) native;
-
-  void set onmessage(EventListener value) { _set_onmessage(this, value); }
-  static void _set_onmessage(var _this, EventListener value) native;
-
   void addEventListener(String type, EventListener listener, [bool useCapture = null]) {
     if (useCapture === null) {
       _addEventListener_MessagePort(this, type, listener);
       return;
     } else {
       _addEventListener_MessagePort_2(this, type, listener, useCapture);
       return;
     }
   }
   static void _addEventListener_MessagePort(receiver, type, listener) native;
@@ skipping 47 matching lines @@
     } else {
       _webkitPostMessage_2(this, message, transfer);
       return;
     }
   }
   static void _webkitPostMessage(receiver, message) native;
   static void _webkitPostMessage_2(receiver, message, transfer) native;
 
   String get typeName() { return "MessagePort"; }
 }