Fix a type error in reify/transformation/builder.dart.

pkg/kernel/lib/transformations/reify/transformation/builder.dart

Index: pkg/kernel/lib/transformations/reify/transformation/builder.dart
diff --git a/pkg/kernel/lib/transformations/reify/transformation/builder.dart b/pkg/kernel/lib/transformations/reify/transformation/builder.dart
index fef0f198b441cc1794ca136ffa04b3289e413187..db46b96e814974efc4192db6ad3760183d9bd31b 100644
--- a/pkg/kernel/lib/transformations/reify/transformation/builder.dart
+++ b/pkg/kernel/lib/transformations/reify/transformation/builder.dart
@@ -443,7 +443,9 @@ class RuntimeTypeSupportBuilder {
           parameter,
           id,
           cls.supertype?.asInterfaceType,
-          cls.implementedTypes.map((Supertype type) => type?.asInterfaceType),
+          cls.implementedTypes
+              .map((Supertype type) => type?.asInterfaceType)
+              .toList(),
           callableType)));
     });