Declare the `$update_count` and `$update_current` properties for `WP_Upgrader`.

See #30224.


git-svn-id: https://develop.svn.wordpress.org/trunk@30171 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/class-wp-upgrader.php

@@ -24,6 +24,8 @@ class WP_Upgrader {
 	public $strings = array();
 	public $skin = null;
 	public $result = array();
+	public $update_count = 0;
+	public $update_current = 0;
 
 	public function __construct($skin = null) {
 		if ( null == $skin )