Skeleton for lexical error recovery.

pkg/dart_scanner/lib/src/array_based_scanner.dart

Index: pkg/dart_scanner/lib/src/array_based_scanner.dart
diff --git a/pkg/dart_scanner/lib/src/array_based_scanner.dart b/pkg/dart_scanner/lib/src/array_based_scanner.dart
index 37b5e3d432ec86d32c959d0329a882e9c3aab11a..d6e9c399a6b26dbff37198e78ae8be3df80bf3bc 100644
--- a/pkg/dart_scanner/lib/src/array_based_scanner.dart
+++ b/pkg/dart_scanner/lib/src/array_based_scanner.dart
@@ -35,6 +35,8 @@ import 'package:compiler_util/link.dart' show
     Link;
 
 abstract class ArrayBasedScanner extends AbstractScanner {
+  bool hasErrors = false;
+
   ArrayBasedScanner(bool includeComments)
       : super(includeComments);
 
@@ -224,6 +226,7 @@ abstract class ArrayBasedScanner extends AbstractScanner {
   }
 
   void appendErrorToken(ErrorToken token) {
+    hasErrors = true;
     tail.next = token;
     tail = token;
   }