Remove more warnings.

lib/compiler/implementation/patch_parser.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.
 
 #library("patchparser");
 #import("dart:uri");
 
 #import("tree/tree.dart", prefix: "tree");
 #import("leg.dart", prefix: 'leg');  // CompilerTask, Compiler.
 #import("apiimpl.dart");
@@ skipping 275 matching lines @@
   void addMember(Element element) {
     if (isMemberPatch || (isClassPatch && element is ClassElement)) {
       element.addMetadata(popMetadata());
     }
     super.addMember(element);
   }
 }
 
 // TODO(ahe): Get rid of this class.
 class PatchMetadataAnnotation extends MetadataAnnotation {
-  final Constant value = null;
+  final leg.Constant value = null;
 
   PatchMetadataAnnotation() : super(STATE_DONE);
 }