fasta.Token implement 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 6aa9a5f6d386823c9a5a6f4892f5088ea2b46b0e..882d35b5cc6a937363578d93659231eb74c449ed 100644
--- a/pkg/front_end/lib/src/fasta/scanner/error_token.dart
+++ b/pkg/front_end/lib/src/fasta/scanner/error_token.dart
@@ -79,6 +79,11 @@ abstract class ErrorToken extends Token {
   int get endOffset => null;
 
   BeginGroupToken get begin => null;
+
+  @override
+  Token copyWithoutComments() {
+    throw 'unsupported operation';
+  }
 }
 
 /// Represents an encoding error.