add fasta.scanner support for lazy assignment operators

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:analyzer/src/fasta/token_utils.dart';
 import 'package:front_end/src/fasta/scanner/error_token.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 10 matching lines @@
     defineReflectiveTests(ScannerTest_Fasta_Roundtrip);
   });
 }
 
 @reflectiveTest
 class ScannerTest_Fasta extends ScannerTestBase {
   @override
   Token scanWithListener(String source, ErrorListener listener,
       {bool genericMethodComments: false,
       bool lazyAssignmentOperators: false}) {
-    // Note: Fasta always supports lazy assignment operators (`&&=` and `||=`),
-    // so we can ignore the `lazyAssignmentOperators` flag.
-    // TODO(paulberry): once lazyAssignmentOperators are fully supported by
-    // Dart, remove this flag.
-    var scanner = new fasta.StringScanner(source, includeComments: true);
-    scanner.scanGenericMethodComments = genericMethodComments;
+    var scanner = new fasta.StringScanner(source,
+        includeComments: true,
+        scanGenericMethodComments: genericMethodComments,
+        scanLazyAssignmentOperators: lazyAssignmentOperators);
     var token = scanner.tokenize();
     return new ToAnalyzerTokenStreamConverter_WithListener(listener)
         .convertTokens(token);
   }
 
-  @override
-  @failingTest
-  void test_ampersand_ampersand_eq() {
-    // TODO(paulberry,ahe): Fasta doesn't support `&&=` yet
-    super.test_ampersand_ampersand_eq();
-  }
-
-  @override
-  @failingTest
-  void test_bar_bar_eq() {
-    // TODO(paulberry,ahe): Fasta doesn't support `||=` yet
-    super.test_bar_bar_eq();
-  }
-
   void test_comments() {
     const source = '''
        /// Doc comment before class
        /// second line
        /// third
        class Foo {
          // Random comment
          Object someField; // trailing comment
          dynamic secondField;
          /// Method doc
@@ skipping 490 matching lines @@
   final ErrorListener _listener;
 
   ToAnalyzerTokenStreamConverter_WithListener(this._listener);
 
   @override
   void reportError(
       ScannerErrorCode errorCode, int offset, List<Object> arguments) {
     _listener.errors.add(new TestError(offset, errorCode, arguments));
   }
 }