init: log when 'user' is unspecified

NOTE: in master, but should be submitted in AOSP.
Waiting to hear from security folks. Also might
need cleanup.

Not currently done. Seems errorprone.

Bug: 276813155
Test: boot, check logs
Change-Id: I7cbc39b282889dd582f06a8eedc38ae637c8edec
diff --git a/init/service_parser.cpp b/init/service_parser.cpp
index 3563084..d89664c 100644
--- a/init/service_parser.cpp
+++ b/init/service_parser.cpp
@@ -534,7 +534,7 @@
     if (!uid.ok()) {
         return Error() << "Unable to find UID for '" << args[1] << "': " << uid.error();
     }
-    service_->proc_attr_.uid = *uid;
+    service_->proc_attr_.parsed_uid = *uid;
     return {};
 }
 
@@ -677,6 +677,11 @@
         return {};
     }
 
+    if (service_->proc_attr_.parsed_uid == std::nullopt) {
+        LOG(WARNING) << "No user specified for service '" << service_->name()
+                     << "'. Defaults to root.";
+    }
+
     if (interface_inheritance_hierarchy_) {
         if (const auto& check_hierarchy_result = CheckInterfaceInheritanceHierarchy(
                     service_->interfaces(), *interface_inheritance_hierarchy_);