[dart2wasm] Fix return type of _typeArguments

This fixes the breakage of barista3 introduced in
https://dart-review.googlesource.com/c/sdk/+/250480

Change-Id: I5ebca17ab35464e0c452d2fbe1b0f6574e05b6cd
Cq-Include-Trybots: luci.dart.try:dart2wasm-linux-x64-d8-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/252381
Reviewed-by: Joshua Litt <joshualitt@google.com>
Commit-Queue: Joshua Litt <joshualitt@google.com>
Auto-Submit: Aske Simon Christensen <askesc@google.com>
diff --git a/sdk/lib/_internal/wasm/lib/object_patch.dart b/sdk/lib/_internal/wasm/lib/object_patch.dart
index 8b727d2..e61e064 100644
--- a/sdk/lib/_internal/wasm/lib/object_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/object_patch.dart
@@ -39,7 +39,7 @@
 
   /// Concrete subclasses of [Object] will have overrides of [_typeArguments]
   /// which return their type arguments.
-  List<Type> get _typeArguments => const [];
+  List<_Type> get _typeArguments => const [];
 
   /// We use [_runtimeType] for internal type testing, because objects can
   /// override [runtimeType].