add support for native methods in class

pkg/front_end/lib/src/fasta/source/stack_listener.dart

Index: pkg/front_end/lib/src/fasta/source/stack_listener.dart
diff --git a/pkg/front_end/lib/src/fasta/source/stack_listener.dart b/pkg/front_end/lib/src/fasta/source/stack_listener.dart
index d7075d0c8c767dfde6eebf9eeafad9ac57fe33c5..bca526938c48f6cead68017c28e4ad077a9ca8c7 100644
--- a/pkg/front_end/lib/src/fasta/source/stack_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/stack_listener.dart
@@ -8,7 +8,11 @@ import 'package:kernel/ast.dart' show AsyncMarker, Expression;
 
 import '../deprecated_problems.dart' show deprecated_inputError;
 
-import '../fasta_codes.dart' show Message, templateInternalProblemStackNotEmpty;
+import '../fasta_codes.dart'
+    show
+        Message,
+        messageNativeClauseShouldBeAnnotation,
+        templateInternalProblemStackNotEmpty;
 
 import '../messages.dart' as messages;
 
@@ -48,6 +52,7 @@ enum NullValue {
   Metadata,
   Modifiers,
   ParameterDefaultValue,
+  StringLiteral,
   SwitchScope,
   Type,
   TypeArguments,
@@ -266,6 +271,7 @@ abstract class StackListener extends Listener {
 
   @override
   void handleRecoverableError(Token token, Message message) {
+    if (message == messageNativeClauseShouldBeAnnotation) return;
     debugEvent("Error: ${message.message}");
     addCompileTimeError(message, token.offset);
   }