Update fasta scanner tests to refer to #28665.

pkg/front_end/test/scanner_fasta_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/error_token.dart' as fasta;
 import 'package:front_end/src/fasta/scanner/keyword.dart' as fasta;
 import 'package:front_end/src/fasta/scanner/string_scanner.dart' as fasta;
 import 'package:front_end/src/fasta/scanner/token.dart' as fasta;
 import 'package:front_end/src/fasta/scanner/token_constants.dart' as fasta;
 import 'package:front_end/src/scanner/errors.dart';
@@ skipping 150 matching lines @@
   @failingTest
   void test_comment_generic_method_type_list() {
     // TODO(paulberry,ahe): Fasta doesn't support generic method comment syntax.
     super.test_comment_generic_method_type_list();
   }
 
   @override
   @failingTest
   void test_index() {
     // TODO(paulberry,ahe): "[]" should be parsed as a single token.
+    // See dartbug.com/28665.
     super.test_index();
   }
 
   @override
   @failingTest
   void test_index_eq() {
     // TODO(paulberry,ahe): "[]=" should be parsed as a single token.
+    // See dartbug.com/28665.
     super.test_index_eq();
   }
 
   @override
   @failingTest
   void test_scriptTag_withArgs() {
     // TODO(paulberry,ahe): script tags are needed by analyzer.
     super.test_scriptTag_withArgs();
   }
 
@@ skipping 330 matching lines @@
         return TokenType.QUESTION_PERIOD;
       case fasta.QUESTION_QUESTION_TOKEN:
         return TokenType.QUESTION_QUESTION;
       case fasta.QUESTION_QUESTION_EQ_TOKEN:
         return TokenType.QUESTION_QUESTION_EQ;
       default:
         throw new UnimplementedError('$kind');
     }
   }
 }