add fasta.scanner support for lazy assignment operators

pkg/front_end/test/scanner_roundtrip_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:analyzer/src/fasta/token_utils.dart';
 import 'package:front_end/src/scanner/errors.dart' as analyzer;
 import 'package:front_end/src/scanner/reader.dart' as analyzer;
 import 'package:front_end/src/scanner/scanner.dart' as analyzer;
 import 'package:front_end/src/scanner/token.dart';
 import 'package:test/test.dart';
@@ skipping 26 matching lines @@
     var fastaToken = fromAnalyzerTokenStream(analyzerToken);
     // Since [scanWithListener] reports errors to the listener, we don't
     // expect any error tokens in the Fasta token stream, so we convert using
     // ToAnalyzerTokenStreamConverter_NoErrors.
     return new ToAnalyzerTokenStreamConverter_NoErrors()
         .convertTokens(fastaToken);
   }
 
   @override
   @failingTest
-  void test_ampersand_ampersand_eq() {
-    // TODO(paulberry,ahe): Fasta scanner doesn't support lazy assignment
-    // operators.
-    super.test_ampersand_ampersand_eq();
-  }
-
-  @override
-  @failingTest
-  void test_bar_bar_eq() {
-    // TODO(paulberry,ahe): Fasta scanner doesn't support lazy assignment
-    // operators.
-    super.test_bar_bar_eq();
-  }
-
-  @override
-  @failingTest
   void test_comment_generic_method_type_assign() {
     // TODO(paulberry,ahe): Fasta scanner doesn't support generic comment
     // syntax.
     super.test_comment_generic_method_type_assign();
   }
 
   @override
   @failingTest
   void test_comment_generic_method_type_list() {
     // TODO(paulberry,ahe): Fasta scanner doesn't support generic comment
     // syntax.
     super.test_comment_generic_method_type_list();
   }
 }
 
 class TestScanner extends analyzer.Scanner {
   TestScanner(analyzer.CharacterReader reader) : super.create(reader);
 
   @override
   void reportError(
       analyzer.ScannerErrorCode errorCode, int offset, List<Object> arguments) {
     fail('Unexpected error $errorCode while scanning offset $offset\n'
         '   arguments: $arguments');
   }
 }