add fasta.scanner support for lazy assignment operators

pkg/front_end/lib/src/fasta/scanner/string_scanner.dart

 // Copyright (c) 2011, 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 dart2js.scanner.string_scanner;
 
 import '../../scanner/token.dart' show TokenType;
 
 import 'array_based_scanner.dart' show ArrayBasedScanner;
 
 import 'token.dart' show CommentToken, DartDocToken, StringToken;
 
 /**
  * Scanner that reads from a String and creates tokens that points to
  * substrings.
  */
 class StringScanner extends ArrayBasedScanner {
   /** The file content. */
   String string;
 
   /** The current offset in [string]. */
   int scanOffset = -1;
 
   StringScanner(String string,
-      {bool includeComments: false, bool scanGenericMethodComments: false})
+      {bool includeComments: false,
+      bool scanGenericMethodComments: false,
+      bool scanLazyAssignmentOperators: false})
       : string = ensureZeroTermination(string),
-        super(includeComments, scanGenericMethodComments);
+        super(includeComments, scanGenericMethodComments,
+            scanLazyAssignmentOperators);
 
   static String ensureZeroTermination(String string) {
     return (string.isEmpty || string.codeUnitAt(string.length - 1) != 0)
         // TODO(lry): abort instead of copying the array, or warn?
         ? string + '\x00'
         : string;
   }
 
   int advance() => string.codeUnitAt(++scanOffset);
   int peek() => string.codeUnitAt(scanOffset + 1);
@@ skipping 40 matching lines @@
 
   SubStringScanner(this.baseOffset, String string,
       {bool includeComments: false})
       : super(string, includeComments: includeComments);
 
   @override
   void beginToken() {
     tokenStart = baseOffset + stringOffset;
   }
 }