Recover from bad supertypes.

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

Index: pkg/front_end/lib/src/fasta/kernel/kernel_type_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_type_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_type_builder.dart
index a1c3b70ea0a33249130b2f24ffb2d4744cab558e..9bee8f900d0d17e57ffb5d10492d948a00409ee0 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_type_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_type_builder.dart
@@ -6,12 +6,12 @@ library fasta.kernel_type_builder;
 
 import 'package:kernel/ast.dart' show DartType, Supertype;
 
-import 'kernel_builder.dart' show TypeBuilder;
+import 'kernel_builder.dart' show LibraryBuilder, TypeBuilder;
 
 abstract class KernelTypeBuilder extends TypeBuilder {
   KernelTypeBuilder(int charOffset, Uri fileUri) : super(charOffset, fileUri);
 
-  DartType build();
+  DartType build(LibraryBuilder library);
 
-  Supertype buildSupertype();
+  Supertype buildSupertype(LibraryBuilder library);
 }