Recover from bad supertypes.

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

Index: pkg/front_end/lib/src/fasta/builder/dynamic_type_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/dynamic_type_builder.dart b/pkg/front_end/lib/src/fasta/builder/dynamic_type_builder.dart
index 5a74165a1b516a4efa1a48549a4798159b7126d5..3933e7c170a97d673dcf4766bc0b0e251bdffaf0 100644
--- a/pkg/front_end/lib/src/fasta/builder/dynamic_type_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/dynamic_type_builder.dart
@@ -13,7 +13,9 @@ class DynamicTypeBuilder<T extends TypeBuilder, R>
   DynamicTypeBuilder(this.type, LibraryBuilder compilationUnit, int charOffset)
       : super(null, 0, "dynamic", compilationUnit, charOffset);
 
-  R buildType(List<T> arguments) => type;
+  R buildType(LibraryBuilder library, List<T> arguments) => type;
 
-  R buildTypesWithBuiltArguments(List<R> arguments) => type;
+  R buildTypesWithBuiltArguments(LibraryBuilder library, List<R> arguments) {
+    return type;
+  }
 }