fix missed rename fasta.Token.value --> lexeme

pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart

 // Copyright (c) 2017, 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:front_end/src/fasta/parser/token_stream_rewriter.dart';
 import 'package:front_end/src/fasta/scanner/precedence.dart';
 import 'package:front_end/src/fasta/scanner/token.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ skipping 92 matching lines @@
   /// token stream.
   ///
   /// The EOF token is returned.
   Token _link(Iterable<Token> tokens) {
     Token head = new SymbolToken(EOF_INFO, -1);
     for (var token in tokens) {
       head.next = token;
       if (setPrevious) token.previousToken = head;
       head = token;
     }
-    int eofOffset = head.charOffset + head.value.length;
+    int eofOffset = head.charOffset + head.lexeme.length;
     if (eofOffset < 0) eofOffset = 0;
     Token eof = new SymbolToken(EOF_INFO, eofOffset);
     head.next = eof;
     if (setPrevious) eof.previousToken = head;
     return eof;
   }
 
   BeginGroupToken _makeBeginGroupToken(int charOffset) {
     return new BeginGroupToken(OPEN_PAREN_INFO, charOffset);
   }
@@ skipping 16 matching lines @@
 /// Concrete implementation of [TokenStreamRewriterTest] in which
 /// [Token.previousToken] values are set to non-null.
 ///
 /// Since [TokenStreamRewriter] makes use of [Token.previousToken] when it can,
 /// these tests do not exercise the more complex heuristics for finding previous
 /// tokens.
 @reflectiveTest
 class TokenStreamRewriterTest_UsingPrevious extends TokenStreamRewriterTest {
   bool get setPrevious => true;
 }