[Merge to M53] arc: Implement safe access to ArcAuthService.

components/user_manager/user_manager_base.cc

Index: components/user_manager/user_manager_base.cc
diff --git a/components/user_manager/user_manager_base.cc b/components/user_manager/user_manager_base.cc
index dead416c0290f7ce0a7edf7f51492bd4f098d679..58d405fb53653808a61b32760cd9b012b4650d2f 100644
--- a/components/user_manager/user_manager_base.cc
+++ b/components/user_manager/user_manager_base.cc
@@ -643,7 +643,8 @@ bool UserManagerBase::IsUserCryptohomeDataEphemeral(
     return true;
 
   // Ephemeral users.
-  if (user && user->GetType() == USER_TYPE_REGULAR &&
+  if (AreEphemeralUsersEnabled() && user &&
+      user->GetType() == USER_TYPE_REGULAR &&
       FindUserInList(account_id) == nullptr) {
     return true;
   }