Refactor DartTypeVisitor and ElementVisitor.

pkg/compiler/lib/src/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 '../constants/expressions.dart';
 import '../tree/tree.dart';
 import '../util/util.dart';
@@ skipping 404 matching lines @@
   void setNative(String name);
 
   Scope buildScope();
 
   void diagnose(Element context, DiagnosticListener listener);
 
   // TODO(johnniwinther): Move this to [AstElement].
   /// Returns the [Element] that holds the [TreeElements] for this element.
   AnalyzableElement get analyzableElement;
 
-  accept(ElementVisitor visitor);
+  accept(ElementVisitor visitor, arg);
 }
 
 class Elements {
   static bool isUnresolved(Element e) {
     return e == null || e.isErroneous;
   }
   static bool isErroneous(Element e) => e != null && e.isErroneous;
 
   /// Unwraps [element] reporting any warnings attached to it, if any.
   static Element unwrap(Element element,
@@ skipping 1190 matching lines @@
   bool get isDeclaredByField;
 
   /// Returns `true` if this member is abstract.
   bool get isAbstract;
 
   /// If abstract, [implementation] points to the overridden concrete member,
   /// if any. Otherwise [implementation] points to the member itself.
   Member get implementation;
 }