Use metadata annotation @patch for patch classes

runtime/lib/deferred_load_patch.dart

 // Copyright (c) 2013, 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.
 
 final Set<String> _loadedLibraries = new Set<String>();
 
-patch class DeferredLibrary {
-  /* patch */ Future<Null> load() {
+@patch class DeferredLibrary {
+  /* @patch */ Future<Null> load() {
     // Dummy implementation that should eventually be replaced by real
     // implementation.
     Future future =
         new Future<Null>.value(null);
     _loadedLibraries.add(libraryName);
     return future;
   }
 }