Part of #1971384: [META] Convert page callbacks to controllers
For instructions on how to convert a page callback into a controller, see the WSCCI Conversion Guide.
Since this is an AJAX callback rather than a full page callback, we should wait on #1944472: Add generic content handler for returning dialogs.
#1944472: Add generic content handler for returning dialogs is in.
I'll take a shot at this
I posted a combined patch at #1987602: Convert ajax_form_callback() to a new style controller.
Drupal is a registered trademark of Dries Buytaert.