Clean up some missing @access tags and other tweaks for 4.0.0-functionality docs.

See #28885.


git-svn-id: https://develop.svn.wordpress.org/trunk@29455 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/class-wp-plugin-install-list-table.php

@@ -25,6 +25,7 @@ class WP_Plugin_Install_List_Table extends WP_List_Table {
 	 * within get_plugins().
 	 *
 	 * @since 4.0.0
+	 * @access protected
 	 */
 	protected function get_installed_plugin_slugs() {
 		$slugs = array();