Use ASTVisitor as in new AST.

compiler/java/com/google/dart/compiler/ast/DartIfStatement.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;
 
 /**
  * Represents a Dart 'if' statement.
  */
 public class DartIfStatement extends DartStatement {
@@ skipping 14 matching lines @@
 
   public DartStatement getElseStatement() {
     return elseStmt;
   }
 
   public DartStatement getThenStatement() {
     return thenStmt;
   }
 
   @Override
-  public void traverse(DartVisitor v, DartContext ctx) {
-    if (v.visit(this, ctx)) {
-      condition = becomeParentOf(v.accept(condition));
-      thenStmt = becomeParentOf(v.accept(thenStmt));
-      if (elseStmt != null) {
-        elseStmt = becomeParentOf(v.accept(elseStmt));
-      }
-    }
-    v.endVisit(this, ctx);
-  }
-
-  @Override
-  public void visitChildren(DartPlainVisitor<?> visitor) {
+  public void visitChildren(ASTVisitor<?> visitor) {
     condition.accept(visitor);
     thenStmt.accept(visitor);
     if (elseStmt != null) {
       elseStmt.accept(visitor);
     }
   }
 
   @Override
-  public <R> R accept(DartPlainVisitor<R> visitor) {
+  public <R> R accept(ASTVisitor<R> visitor) {
     return visitor.visitIfStatement(this);
   }
 }