admin_head-media-upload-popup WordPress Action Hook
The admin_head-media-upload-popup hook is a hook that is run when the WordPress media upload popup is displayed in the admin interface. This hook can be used to add custom CSS or JavaScript to the popup.
do_action( 'admin_head-media-upload-popup' ) #
Fires when scripts enqueued for the admin header for the legacy (pre-3.5.0) media upload popup are printed.