Minor fixes in dart2js.

lib/compiler/implementation/tree/nodes.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 Visitor<R> {
   const Visitor();
 
   abstract R visitNode(Node node);
 
   R visitBlock(Block node) => visitStatement(node);
@@ skipping 1106 matching lines @@
   }
 
   Token getBeginToken() => beginToken;
 
   Token getEndToken() => beginToken.endGroup;
 }
 
 /** Representation of modifiers such as static, abstract, final, etc. */
 class Modifiers extends Node {
   /**
-   * Pseudo-constant for empty modifiers. Use this instead of null.
+   * Pseudo-constant for empty modifiers.
    */
   static final Modifiers EMPTY = new Modifiers(new NodeList.empty());
 
   /* TODO(ahe): The following should be validated relating to modifiers:
    * 1. The nodes must come in a certain order.
    * 2. The keywords "var" and "final" may not be used at the same time.
    * 3. The keywords "abstract" and "external" may not be used at the same time.
    * 4. The type of an element must be null if isVar() is true.
    */
 
@@ skipping 813 matching lines @@
  * argument).
  *
  * TODO(ahe): This method is controversial, the team needs to discuss
  * if top-level methods are acceptable and what naming conventions to
  * use.
  */
 initializerDo(Node node, f(Node node)) {
   SendSet send = node.asSendSet();
   if (send !== null) return f(send.arguments.head);
 }