Recover from bad supertypes.

pkg/front_end/lib/src/fasta/builder/type_declaration_builder.dart

Index: pkg/front_end/lib/src/fasta/builder/type_declaration_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/type_declaration_builder.dart b/pkg/front_end/lib/src/fasta/builder/type_declaration_builder.dart
index e0cc77191e7c5e9c3597e75a2def9e76abe4f584..0053c44339cadadc1113f9a88090938be47d5b3a 100644
--- a/pkg/front_end/lib/src/fasta/builder/type_declaration_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/type_declaration_builder.dart
@@ -5,7 +5,7 @@
 library fasta.type_declaration_builder;
 
 import 'builder.dart'
-    show Builder, MetadataBuilder, ModifierBuilder, TypeBuilder;
+    show Builder, LibraryBuilder, MetadataBuilder, ModifierBuilder, TypeBuilder;
 
 import '../util/relativize.dart' show relativizeUri;
 
@@ -32,8 +32,10 @@ abstract class TypeDeclarationBuilder<T extends TypeBuilder, R>
 
   bool get isTypeDeclaration => true;
 
-  R buildType(List<T> arguments);
+  bool get isTypeVariable => false;
+
+  R buildType(LibraryBuilder library, List<T> arguments);
 
   /// [arguments] have already been built.
-  R buildTypesWithBuiltArguments(List<R> arguments);
+  R buildTypesWithBuiltArguments(LibraryBuilder library, List<R> arguments);
 }