Joomla auto-save of features fails due to missing JavaScript file

On most Joomla permissions config pages (e.g., /administrator/index.php?option=com_config&view=component&component=com_cache), changing the value of a permission will cause the permission setting to be saved immediately, as shown by a green check-box next to the field (depending on the theme, I guess), and as shown by reloading the page and observing the changed field value.

On CiviCRM Configuration "Permissions" tab (/administrator/index.php?option=com_config&view=component&component=com_civicrm) changing the value of a permission field triggers a JavaScript error: 

Uncaught ReferenceError: sendPermissions is not defined

This is caused by the absence of the js file system/js/permissions.js, due to what I think is incorrect use of JHtml::_(). I'll post a PR that fixes this momentarily, but it would be good if someone more experienced with Joomla could review it.