flag to enable fasta scanner in analyzer

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

Index: pkg/front_end/lib/src/scanner/reader.dart
diff --git a/pkg/front_end/lib/src/scanner/reader.dart b/pkg/front_end/lib/src/scanner/reader.dart
index b0791396e4f703e914258edce7ecb6e6d8b3bbbe..d0cc35219c3a4e3a874b1dff1c9df41f21207da9 100644
--- a/pkg/front_end/lib/src/scanner/reader.dart
+++ b/pkg/front_end/lib/src/scanner/reader.dart
@@ -28,6 +28,11 @@ abstract class CharacterReader {
   int advance();
 
   /**
+   * Return the source to be scanned.
+   */
+  String getContents();
+
+  /**
    * Return the substring of the source code between the [start] offset and the
    * modified current position. The current position is modified by adding the
    * [endDelta], which is the number of characters after the current location to
@@ -88,6 +93,9 @@ class CharSequenceReader implements CharacterReader {
   }
 
   @override
+  String getContents() => _sequence;
+
+  @override
   String getString(int start, int endDelta) =>
       _sequence.substring(start, _charOffset + endDelta);
 
@@ -128,6 +136,9 @@ class SubSequenceReader extends CharSequenceReader {
   }
 
   @override
+  String getContents() => super.getContents().substring(_offsetDelta);
+
+  @override
   String getString(int start, int endDelta) =>
       super.getString(start - _offsetDelta, endDelta);
 }