Complain about duplicated names.

pkg/front_end/lib/src/fasta/kernel/fasta_accessors.dart

Index: pkg/front_end/lib/src/fasta/kernel/fasta_accessors.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/fasta_accessors.dart b/pkg/front_end/lib/src/fasta/kernel/fasta_accessors.dart
index a0ead8b18c1a844cd47929790fc3b8b189bc266a..2ee76f7d90a912a84550112e4cf9e0ba587d93ec 100644
--- a/pkg/front_end/lib/src/fasta/kernel/fasta_accessors.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/fasta_accessors.dart
@@ -87,6 +87,9 @@ abstract class BuilderHelper {
       List<TypeParameter> typeParameters);
 
   StaticGet makeStaticGet(Member readTarget, Token token);
+
+  dynamic addCompileTimeError(int charOffset, String message,
+      {bool silent: false});
 }
 
 abstract class FastaAccessor implements Accessor {