Remove AbstractVisitor.

dart/lib/compiler/implementation/resolver.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.
 
 abstract class TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
   DartType getType(TypeAnnotation annotation);
   bool isParameterChecked(Element element);
 }
@@ skipping 686 matching lines @@
         error(link.head, MessageKind.INVALID_INITIALIZER);
       }
     }
     if (!resolvedSuper) {
       resolveImplicitSuperConstructorSend(constructor, functionNode);
     }
     return null;  // If there was no redirection always return null.
   }
 }
 
-class CommonResolverVisitor<R> extends AbstractVisitor<R> {
+class CommonResolverVisitor<R> extends Visitor<R> {
   final Compiler compiler;
 
   CommonResolverVisitor(Compiler this.compiler);
 
   R visitNode(Node node) {
     cancel(node,
            'internal error: Unhandled node: ${node.getObjectDescription()}');
   }
 
   R visitEmptyStatement(Node node) => null;
@@ skipping 2162 matching lines @@
 
   Element localLookup(SourceString name) => library.find(name);
   Element lookup(SourceString name) => localLookup(name);
   Element lexicalLookup(SourceString name) => localLookup(name);
 
   Element add(Element newElement) {
     throw "Cannot add an element in the top scope";
   }
   String toString() => '$element';
 }