more work aligning fasta.Token with analyzer.Token

pkg/front_end/lib/src/fasta/scanner/error_token.dart

Index: pkg/front_end/lib/src/fasta/scanner/error_token.dart
diff --git a/pkg/front_end/lib/src/fasta/scanner/error_token.dart b/pkg/front_end/lib/src/fasta/scanner/error_token.dart
index 84a7ec61e0530b6bcec923df34e60a36949a09e0..6fe80fe12fabbaf1abc622c84555170e78e02014 100644
--- a/pkg/front_end/lib/src/fasta/scanner/error_token.dart
+++ b/pkg/front_end/lib/src/fasta/scanner/error_token.dart
@@ -71,6 +71,11 @@ abstract class ErrorToken extends Token {
 
   TokenType get type => TokenType.BAD_INPUT;
 
+  /// This is a token that wraps around an error message. Return 1
+  /// instead of the size of the length of the error message.
+  @override
+  int get charCount => 1;
+
   String get lexeme => throw assertionMessage;
 
   bool get isIdentifier => false;