Use metadata annotation @patch for patch classes

runtime/lib/map_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 Map<K, V> {
+@patch class Map<K, V> {
   // Factory constructing a Map from a parser generated Map literal.
   // [elements] contains n key-value pairs.
   // The keys are at position 2*n and are already type checked by the parser
   // in checked mode.
   // The values are at position 2*n+1 and are not yet type checked.
   factory Map._fromLiteral(List elements) {
     var map = new LinkedHashMap<K, V>();
     var len = elements.length;
     for (int i = 1; i < len; i += 2) {
       map[elements[i - 1]] = elements[i];
     }
     return map;
   }
 
-  /* patch */ factory Map.unmodifiable(Map other) {
+  /* @patch */ factory Map.unmodifiable(Map other) {
     return new UnmodifiableMapView<K, V>(new Map.from(other));
   }
 
-  /* patch */ factory Map() = LinkedHashMap<K, V>;
+  /* @patch */ factory Map() = LinkedHashMap<K, V>;
 }