Index: src/wp-admin/includes/class-automatic-upgrader-skin.php
===================================================================
--- src/wp-admin/includes/class-automatic-upgrader-skin.php	(revision 51489)
+++ src/wp-admin/includes/class-automatic-upgrader-skin.php	(working copy)
@@ -19,6 +19,14 @@
  * @see Bulk_Upgrader_Skin
  */
 class Automatic_Upgrader_Skin extends WP_Upgrader_Skin {
+
+	/**
+	 * Holds internal messages for this class.
+	 *
+	 * @since 3.7.0
+	 *
+	 * @var array
+	 */
 	protected $messages = array();
 
 	/**