fix fasta/analyzer KeywordToken.value()

pkg/front_end/lib/src/fasta/scanner/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.
 
 library fasta.scanner.token;
 
 import '../../scanner/token.dart' as analyzer;
 
 import 'keyword.dart' show Keyword;
 
@@ skipping 341 matching lines @@
 
   bool get isBuiltInIdentifier => keyword.isBuiltIn;
 
   String toString() => "KeywordToken($lexeme)";
 
   @override
   Token copyWithoutComments() => new KeywordToken(keyword, charOffset);
 
   @override
   // Analyzer considers pseudo-keywords to have a different value
-  Keyword value() => isPseudo ? lexeme : keyword;
+  Object value() => isPseudo ? lexeme : keyword;
 
   @override
   // Analyzer considers pseudo-keywords to be identifiers
   analyzer.TokenType get type => isPseudo ? IDENTIFIER_INFO : KEYWORD_INFO;
 }
 
 /**
  * A synthetic keyword token.
  */
 class SyntheticKeywordToken extends KeywordToken
@@ skipping 320 matching lines @@
       identical(value, "<=") ||
       identical(value, "<") ||
       identical(value, "&") ||
       identical(value, "^") ||
       identical(value, "|");
 }
 
 bool isTernaryOperator(String value) => identical(value, "[]=");
 
 bool isMinusOperator(String value) => identical(value, "-");