add fasta.scanner support for lazy assignment operators

pkg/analyzer/lib/src/dart/scanner/scanner.dart

 // Copyright (c) 2014, 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 analyzer.src.dart.scanner.scanner;
 
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/src/dart/error/syntactic_errors.dart';
 import 'package:analyzer/src/dart/scanner/reader.dart';
@@ skipping 129 matching lines @@
 
   @override
   Token tokenize() {
     // Note: Fasta always supports lazy assignment operators (`&&=` and `||=`),
     // so we can ignore the `scanLazyAssignmentOperators` flag.
     if (scanGenericMethodComments) {
       // Fasta doesn't support generic method comments.
       // TODO(danrubel): remove this once fasts support has been added.
       throw 'No generic method comment support in Fasta';
     }
-    fasta.ScannerResult result =
-        fasta.scanString(_contents, includeComments: _preserveComments);
+    fasta.ScannerResult result = fasta.scanString(_contents,
+        includeComments: _preserveComments,
+        scanLazyAssignmentOperators: scanLazyAssignmentOperators);
     // fasta pretends there is an additional line at EOF
     lineStarts
         .addAll(result.lineStarts.sublist(1, result.lineStarts.length - 1));
     fasta.Token token = result.tokens;
     // The default recovery strategy used by scanString
     // places all error tokens at the head of the stream.
     while (token.type == TokenType.BAD_INPUT) {
       translateErrorToken(token, reportError);
       token = token.next;
     }
     firstToken = token;
     return firstToken;
   }
 
   @override
   set preserveComments(bool preserveComments) {
     this._preserveComments = preserveComments;
   }
 }