flag to enable fasta scanner in analyzer

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

Index: pkg/analyzer/lib/src/dart/scanner/reader.dart
diff --git a/pkg/analyzer/lib/src/dart/scanner/reader.dart b/pkg/analyzer/lib/src/dart/scanner/reader.dart
index 6e111e266756abeaac09e260bedb14e98595fe6b..2b49cd77ef3b162182bf9cf8381b23994413d446 100644
--- a/pkg/analyzer/lib/src/dart/scanner/reader.dart
+++ b/pkg/analyzer/lib/src/dart/scanner/reader.dart
@@ -20,6 +20,11 @@ class CharacterRangeReader extends CharacterReader {
   final CharacterReader baseReader;
 
   /**
+   * The first character to be read.
+   */
+  final int startIndex;
+
+  /**
    * The last character to be read.
    */
   final int endIndex;
@@ -28,7 +33,7 @@ class CharacterRangeReader extends CharacterReader {
    * Initialize a newly created reader to read the characters from the given
    * [baseReader] between the [startIndex] inclusive to [endIndex] exclusive.
    */
-  CharacterRangeReader(this.baseReader, int startIndex, this.endIndex) {
+  CharacterRangeReader(this.baseReader, this.startIndex, this.endIndex) {
     baseReader.offset = startIndex - 1;
   }
 
@@ -49,6 +54,10 @@ class CharacterRangeReader extends CharacterReader {
   }
 
   @override
+  String getContents() =>
+      baseReader.getContents().substring(startIndex, endIndex);
+
+  @override
   String getString(int start, int endDelta) =>
       baseReader.getString(start, endDelta);