WP_Media_List_Table::get_sortable_columns()

	protected function get_sortable_columns() {
		return array(
			'title'    => 'title',
			'author'   => 'author',
			'parent'   => 'parent',
			'comments' => 'comment_count',
			'date'     => array( 'date', true ),
		);
	}