cleanup to Value - fix for StringEscapesTest

frog/token.dart

 // 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.
 
 /**
  * A single token in the Dart language.
  */
 class Token {
   /** A member of [TokenKind] specifying what kind of token this is. */
   final int kind;
@@ skipping 27 matching lines @@
       return kindText;
     }
   }
 
   /** Returns a [SourceSpan] representing the source location. */
   SourceSpan get span() {
     return new SourceSpan(source, start, end);
   }
 }
 
+/** A token containing a parsed literal value. */
+class LiteralToken extends Token {
+  var value;
+  LiteralToken(kind, source, start, end, this.value)
+      : super(kind, source, start, end);
+}
+
 /** A token containing error information. */
 class ErrorToken extends Token {
   String message;
   ErrorToken(kind, source, start, end, this.message)
       : super(kind, source, start, end);
 }