flag to enable fasta scanner in analyzer

pkg/front_end/lib/src/dependency_grapher_impl.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 'dart:async';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/src/dart/scanner/reader.dart';
 import 'package:analyzer/src/generated/parser.dart';
@@ skipping 23 matching lines @@
   var startingPoint = new _StartingPoint(walker, sources);
   await walker.walk(startingPoint);
   return walker.graph;
 }
 
 /// Type of the callback function used by [graphForProgram] to read file
 /// contents.
 typedef Future<String> FileReader(Uri originalUri, Uri resolvedUri);
 
 class _Scanner extends Scanner {
-  _Scanner(String contents) : super(new CharSequenceReader(contents)) {
+  _Scanner(String contents) : super.create(new CharSequenceReader(contents)) {
     preserveComments = false;
   }
 
   @override
   void reportError(errorCode, int offset, List<Object> arguments) {
     // TODO(paulberry): report errors.
   }
 }
 
 class _StartingPoint extends _WalkerNode {
@@ skipping 87 matching lines @@
           handleDependency(referencedUri);
         }
       }
     }
     if (!coreUriFound) {
       handleDependency(dartCoreUri);
     }
     return dependencies;
   }
 }