Properly generate MutationCallback in dart:html.

lib/dom/dom.dart

 #library('dom');
 
 // 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.
 
 // DO NOT EDIT
 // Auto-generated Dart DOM library with no implementation.
 
 
@@ skipping 5994 matching lines @@
   final int y;
 
   void initMouseEvent(String type, bool canBubble, bool cancelable, DOMWindow view, int detail, int screenX, int screenY, int clientX, int clientY, bool ctrlKey, bool altKey, bool shiftKey, bool metaKey, int button, EventTarget relatedTarget);
 }
 // 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.
 
 // WARNING: Do not edit - generated code.
 
-interface MutationCallback {
-}
+typedef bool MutationCallback(List<MutationRecord> mutations, WebKitMutationObserver observer);
 // 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.
 
 // WARNING: Do not edit - generated code.
 
 interface MutationEvent extends Event {
 
   static final int ADDITION = 2;
 
@@ skipping 6933 matching lines @@
 // 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.
 
 Window get window() => _dummy();
 
 // TODO(vsm): Remove when prefixes are supported.
 Window get dom_window() => _dummy();
 
 Document get document() => _dummy();