Fix ElementVisitor

sdk/lib/_internal/compiler/implementation/elements/elements.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 elements;
 
 
 import '../tree/tree.dart';
 import '../util/util.dart';
 import '../resolution/resolution.dart';
@@ skipping 242 matching lines @@
 
   Scope buildScope();
 
   /// If the element is a forwarding constructor, [targetConstructor] holds
   /// the generative constructor that the forwarding constructor points to
   /// (possibly via other forwarding constructors).
   FunctionElement get targetConstructor;
 
   void diagnose(Element context, DiagnosticListener listener);
 
-  accept(ElementVisitor visitor) => visitor.visitElement(this);
+  accept(ElementVisitor visitor);
 }
 
 class Elements {
   static bool isUnresolved(Element e) {
     return e == null || e.isErroneous();
   }
   static bool isErroneousElement(Element e) => e != null && e.isErroneous();
 
   /// Unwraps [element] reporting any warnings attached to it, if any.
   static Element unwrap(Element element,
@@ skipping 713 matching lines @@
   int get resolutionState;
   Token get beginToken;
   Token get endToken;
 
   // TODO(kasperl): Try to get rid of these.
   void set annotatedElement(Element value);
   void set resolutionState(int value);
 
   MetadataAnnotation ensureResolved(Compiler compiler);
 }
+
+abstract class VoidElement extends Element {}