flatten Keyword into TokenType

pkg/front_end/test/precedence_info_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/scanner/string_scanner.dart';
 import 'package:front_end/src/fasta/scanner/token.dart' as fasta;
 import 'package:front_end/src/scanner/token.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ skipping 371 matching lines @@
   void test_type() {
     void assertLexeme(String source, TokenType tt) {
       var scanner = new StringScanner(source, includeComments: true);
       var token = scanner.tokenize();
       expect(token.type, same(tt), reason: source);
     }
 
     assertLexeme('1.0', TokenType.DOUBLE);
     assertLexeme('0xA', TokenType.HEXADECIMAL);
     assertLexeme('1', TokenType.INT);
-    assertLexeme('var', TokenType.KEYWORD);
+    assertLexeme('var', Keyword.VAR);
     assertLexeme('#!/', TokenType.SCRIPT_TAG);
+    assertLexeme('foo', TokenType.IDENTIFIER);
     assertLexeme('"foo"', TokenType.STRING);
   }
 }