The only PHP code here is this:
// Fetch the upload progress data
$status = uploadprogress_get_info($_GET['uid']);
// Calculate the current percentage
// If there is no data, assume it's done
Which looks correct to me. Beyond that there is a couple of configuration changes you need to hook it in.
As of 5.4, this library is no longer required since you can poll the sessions instead. The only thing you need to really do is verify that that PHP is working as expected. This will not be as easy as it sounds though; since the http is stateless, the only thing direct access can tell you is if the functions exist. Beyond that, you'll need to probably run a socket or curl test in order to test it out.