Use ASTVisitor as in new AST.

compiler/java/com/google/dart/compiler/ast/DartFunction.java

 // Copyright (c) 2011, 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.
 
 package com.google.dart.compiler.ast;
 
 import java.util.List;
 
 /**
  * Represents a Dart function.
@@ skipping 19 matching lines @@
   }
 
   public List<DartParameter> getParams() {
     return params;
   }
 
   public DartTypeNode getReturnTypeNode() {
     return returnTypeNode;
   }
 
-  public void traverse(DartVisitor v, DartContext ctx) {
-    if (v.visit(this, ctx)) {
-      v.acceptWithInsertRemove(this, params);
-      if (body != null) {
-        body = becomeParentOf(v.accept(body));
-      }
-      if (returnTypeNode != null) {
-        returnTypeNode = becomeParentOf(v.accept(returnTypeNode));
-      }
-    }
-    v.endVisit(this, ctx);
-  }
-
   @Override
-  public void visitChildren(DartPlainVisitor<?> visitor) {
+  public void visitChildren(ASTVisitor<?> visitor) {
     visitor.visit(params);
     if (body != null) {
       body.accept(visitor);
     }
     if (returnTypeNode != null) {
       returnTypeNode.accept(visitor);
     }
   }
 
   @Override
-  public <R> R accept(DartPlainVisitor<R> visitor) {
+  public <R> R accept(ASTVisitor<R> visitor) {
     return visitor.visitFunction(this);
   }
 }