flag to enable fasta scanner in analyzer

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

 // Copyright (c) 2016, 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:charcode/ascii.dart';
 import 'package:front_end/src/scanner/errors.dart';
 import 'package:front_end/src/scanner/reader.dart';
 import 'package:front_end/src/scanner/string_utilities.dart';
 import 'package:front_end/src/scanner/token.dart';
 
@@ skipping 184 matching lines @@
   /**
    * A flag indicating whether the lazy compound assignment operators '&&=' and
    * '||=' are enabled.
    */
   bool scanLazyAssignmentOperators = false;
 
   /**
    * Initialize a newly created scanner to scan characters from the given
    * character [_reader].
    */
-  Scanner(this._reader) {
+  Scanner.create(this._reader) {
     _tokens = new Token(TokenType.EOF, -1);
     _tokens.setNext(_tokens);
     _tail = _tokens;
     _tokenStart = -1;
     _lineStarts.add(0);
   }
 
   /**
    * Return the first token in the token stream that was scanned.
    */
@@ skipping 1116 matching lines @@
   }
 
   /**
    * Checks if [value] is a single-line or multi-line comment.
    */
   static bool _isDocumentationComment(String value) {
     return StringUtilities.startsWith3(value, 0, $slash, $slash, $slash) ||
         StringUtilities.startsWith3(value, 0, $slash, $asterisk, $asterisk);
   }
 }