Ensure a class is finalized before attempting any reflective invocation on it.

runtime/lib/mirrors.cc

Index: runtime/lib/mirrors.cc
diff --git a/runtime/lib/mirrors.cc b/runtime/lib/mirrors.cc
index fe4ccf065978ca01834ee4724775d515a6663cc2..ac558b171d8f5a4d0b6f11cc1d2e255748462da0 100644
--- a/runtime/lib/mirrors.cc
+++ b/runtime/lib/mirrors.cc
@@ -337,6 +337,12 @@ static RawInstance* CreateClassMirror(const Class& cls,
     }
   }
 
+  const Error& error = Error::Handle(cls.EnsureIsFinalized(Isolate::Current()));
+  if (!error.IsNull()) {
+    ThrowInvokeError(error);
+    UNREACHABLE();
+  }
+
   const Bool& is_generic = Bool::Get(cls.NumTypeParameters() != 0);
   const Bool& is_mixin_app_alias = Bool::Get(cls.is_mixin_app_alias());