Make the VM's dart:core and dart:async library patches clean.

runtime/lib/bool_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.
 
 // Dart core library.
 
 @patch class bool {
 
   @patch const factory bool.fromEnvironment(String name,
                                             {bool defaultValue: false})
       native "Bool_fromEnvironment";
 
+  @patch
   int get hashCode => this ? 1231 : 1237;
+
   int get _identityHashCode => this ? 1231 : 1237;
 }