Use metadata annotation @patch for patch classes

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([String this.name])
+@patch class Expando<T> {
+  /* @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) {
+  /* @patch */ T operator[](Object object) {
     _checkType(object);
 
     var mask = _size - 1;
     var idx = object._identityHashCode & mask;
     var wp = _data[idx];
 
     while (wp != null) {
       if (identical(wp.key, object)) {
         return wp.value;
       } else if (wp.key == null) {
         // This entry has been cleared by the GC.
         _data[idx] = _deletedEntry;
       }
       idx = (idx + 1) & mask;
       wp = _data[idx];
     }
 
     return null;
   }
 
-  /* patch */ void operator[]=(Object object, T value) {
+  /* @patch */ void operator[]=(Object object, T value) {
     _checkType(object);
 
     var mask = _size - 1;
     var idx = object._identityHashCode & mask;
     var empty_idx = -1;
     var wp = _data[idx];
 
     while (wp != null) {
       if (identical(wp.key, object)) {
         if (value != null) {
@@ skipping 90 matching lines @@
           "Expandos are not allowed on strings, numbers, booleans or null");
     }
   }
 
   get _size => _data.length;
   get _limit => (3 * (_size ~/ 4));
 
   List _data;
   int _used;  // Number of used (active and deleted) slots.
 }