$this
See #51800, #52217 Fixes #52243 Built from https://develop.svn.wordpress.org/trunk@49946 git-svn-id: http://core.svn.wordpress.org/trunk@49645 1a063a9b-81f0-0310-95a4-ce76da25c4cd
$type
$mime_type
WP_Customize_Image_Control
$button_labels
WP_Customize_Upload_Control
@since
class-wp-widget-area-customize-control.php