Use ASTVisitor as in new AST.

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

Index: compiler/java/com/google/dart/compiler/ast/DartVisitable.java
diff --git a/compiler/java/com/google/dart/compiler/ast/DartVisitable.java b/compiler/java/com/google/dart/compiler/ast/DartVisitable.java
deleted file mode 100644
index 56e0ddafe9ae63621e58d214d19dfb077506b5bc..0000000000000000000000000000000000000000
--- a/compiler/java/com/google/dart/compiler/ast/DartVisitable.java
+++ /dev/null
@@ -1,19 +0,0 @@
-// 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;
-
-/**
- * Interface to be implemented by a class that can be visited by {@link DartVisitor}.
- */
-public interface DartVisitable {
-
-  /**
-   * Causes this object to have the visitor visit itself and its children.
-   *
-   * @param visitor the visitor that should traverse this node
-   * @param ctx the context of an existing traversal
-   */
-  void traverse(DartVisitor v, DartContext ctx);
-}