integrating fasta parser

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 30 matching lines @@
 
   /**
    * Initialize a newly created scanner to scan characters from the given
    * [source]. The given character [reader] will be used to read the characters
    * in the source. The given [_errorListener] will be informed of any errors
    * that are found.
    */
   factory Scanner(Source source, CharacterReader reader,
           AnalysisErrorListener errorListener) =>
       fe.Scanner.useFasta
-          ? new _Scanner2(
-              source, reader.getContents(), reader.offset, errorListener)
+          ? new Scanner.fasta(source, errorListener,
+              contents: reader.getContents(), offset: reader.offset)
           : new Scanner._(source, reader, errorListener);
 
+  factory Scanner.fasta(Source source, AnalysisErrorListener errorListener,
+      {String contents, int offset: 0}) {
+    return new _Scanner2(
+        source, contents ?? source.contents.data, offset, errorListener);
+  }
+
   Scanner._(this.source, CharacterReader reader, this._errorListener)
       : super.create(reader);
 
   @override
   void reportError(
       ScannerErrorCode errorCode, int offset, List<Object> arguments) {
     _errorListener
         .onError(new AnalysisError(source, offset, 1, errorCode, arguments));
   }
 }
@@ skipping 119 matching lines @@
     if (_readerOffset != -1) {
       final int delta = _readerOffset + 1;
       do {
         token.offset += delta;
         token = token.next;
       } while (!token.isEof);
     }
     return firstToken;
   }
 }