Implement updated method overriding rules in the vm.

runtime/lib/expando_patch.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.
 
 patch class Expando<T> {
-  /* patch */ Expando([this.name])
+  /* patch */ Expando([String this.name])
       : _data = new List(_minSize),
         _used = 0;
 
   static const _minSize = 8;
   static final _deletedEntry = new _WeakProperty(null, null);
 
   /* patch */ T operator[](Object object) {
     _checkType(object);
 
     var mask = _size - 1;
@@ skipping 117 matching lines @@
       throw new ArgumentError(object);
     }
   }
 
   get _size => _data.length;
   get _limit => (3 * (_size ~/ 4));
 
   List _data;
   int _used;  // Number of used (active and deleted) slots.
 }