fixes #131, use before define from variables to classes

lib/src/js/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.
 
 part of js_ast;
 
 abstract class NodeVisitor<T> {
   T visitProgram(Program node);
 
   T visitBlock(Block node);
@@ skipping 1062 matching lines @@
    *
    * The constructor does not add the required quotes.  If [value] is not
    * surrounded by quotes and property escaped, the resulting object is invalid
    * as a JS value.
    *
    * TODO(sra): Introduce variants for known valid strings that don't allocate a
    * new string just to add quotes.
    */
   LiteralString(this.value);
 
+  /// Gets the value inside the string without the beginning and end quotes.
+  String get valueWithoutQuotes => value.substring(1, value.length - 1);
+
   accept(NodeVisitor visitor) => visitor.visitLiteralString(this);
   LiteralString _clone() => new LiteralString(value);
 }
 
 class LiteralNumber extends Literal {
   final String value;  // Must be a valid JavaScript number literal.
 
   LiteralNumber(this.value);
 
   accept(NodeVisitor visitor) => visitor.visitLiteralNumber(this);
@@ skipping 344 matching lines @@
   final Expression expression;
 
   CommentExpression(this.comment, this.expression);
 
   int get precedenceLevel => PRIMARY;
   accept(NodeVisitor visitor) => visitor.visitCommentExpression(this);
   CommentExpression _clone() => new CommentExpression(comment, expression);
 
   void visitChildren(NodeVisitor visitor) => expression.accept(visitor);
 }