integrating fasta parser

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

Index: pkg/analyzer/lib/src/dart/scanner/scanner.dart
diff --git a/pkg/analyzer/lib/src/dart/scanner/scanner.dart b/pkg/analyzer/lib/src/dart/scanner/scanner.dart
index fba9b6321c3808347ae41cd25b5cb5401617043c..ad20ed23f7f29cb16712b176f04d3aba5d6bbb2e 100644
--- a/pkg/analyzer/lib/src/dart/scanner/scanner.dart
+++ b/pkg/analyzer/lib/src/dart/scanner/scanner.dart
@@ -48,10 +48,16 @@ class Scanner extends fe.Scanner {
   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);