Support metadata on patches.

pkg/compiler/lib/src/js_backend/constant_handler_javascript.dart

 // Copyright (c) 2014, 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.
 
 part of js_backend;
 
 /// [ConstantCompilerTask] for compilation of constants for the JavaScript
 /// backend.
 ///
 /// Since this task needs to distinguish between frontend and backend constants
@@ skipping 243 matching lines @@
       element.node.accept(new ForgetConstantNodeVisitor(this));
     }
   }
 }
 
 class ForgetConstantElementVisitor
     extends BaseElementVisitor<dynamic, JavaScriptConstantCompiler> {
   const ForgetConstantElementVisitor();
 
   void visitElement(Element e, JavaScriptConstantCompiler constants) {
-    for (MetadataAnnotation data in e.metadata) {
+    for (MetadataAnnotation data in e.implementation.metadata) {
       constants.metadataConstantMap.remove(data);
       if (data.hasNode) {
         data.node.accept(new ForgetConstantNodeVisitor(constants));
       }
     }
   }
 
   void visitFunctionElement(FunctionElement e,
                             JavaScriptConstantCompiler constants) {
     super.visitFunctionElement(e, constants);
@@ skipping 15 matching lines @@
     // TODO(ahe): This doesn't belong here. Rename this class and generalize.
     var closureClassMap =
         constants.compiler.closureToClassMapper.closureMappingCache
         .remove(node);
     if (closureClassMap != null) {
       closureClassMap.removeMyselfFrom(
           constants.compiler.enqueuer.codegen.universe);
     }
   }
 }