rename fasta.Token.value --> lexeme

tests/compiler/dart2js/scanner_offset_length_test.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.
 
 import "package:expect/expect.dart";
 import 'package:front_end/src/fasta/scanner.dart';
 
 Token scan(String text) =>
     new StringScanner(text, includeComments: true).tokenize();
 
 check(String text) {
   Token token = scan(text);
   while (token.kind != EOF_TOKEN) {
-    Expect.equals(token.value.length, token.charCount);
+    Expect.equals(token.lexeme.length, token.charCount);
 
     var start = token.charOffset;
     var end = token.charOffset + token.charCount;
 
     Expect.isTrue(start < text.length,
         'start=$start < text.length=${text.length}: $text');
 
     Expect.isTrue(
         end <= text.length, 'end=$end <= text.length=${text.length}: $text');
 
     Expect.isTrue(start <= end, 'start=$end <= end=$end: $text');
 
     var substring = text.substring(start, end);
 
     Expect.stringEquals(
-        token.value,
+        token.lexeme,
         substring,
-        'token.value=${token.value} == '
+        'token.value=${token.lexeme} == '
         'text.substring(start,end)=${substring}: $text');
 
     print('$text: [$start,$end]:$token');
 
     token = token.next;
   }
 }
 
 main() {
   check('foo'); // identifier
   check('\'\''); // empty string
   check('\'foo\''); // simple string
   check('\'\$foo\''); // interpolation, identifier
   check('\'\${foo}\''); // interpolation, expression
 
   check('//'); // single line comment
   check('/**/'); // multi line comment
 }