Language Upgrader: Re-use the automatic upgrader skin if the parent upgrader is using it.

Prevents broken Ajax responses when `Language_Pack_Upgrader::async_upgrade()` gets triggered during a shiny update.

Fixes #34048.
Built from https://develop.svn.wordpress.org/trunk@34748


git-svn-id: http://core.svn.wordpress.org/trunk@34713 1a063a9b-81f0-0310-95a4-ce76da25c4cd

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

@@ -1867,9 +1867,14 @@ class Language_Pack_Upgrader extends WP_Upgrader {
 			return;
 		}
 
+		// Re-use the automatic upgrader skin if the parent upgrader is using it.
+		if ( $upgrader && $upgrader->skin instanceof Automatic_Upgrader_Skin ) {
+			$skin = $upgrader->skin;
+		} else {
 			$skin = new Language_Pack_Upgrader_Skin( array(
 				'skip_header_footer' => true,
 			) );
+		}
 
 		$lp_upgrader = new Language_Pack_Upgrader( $skin );
 		$lp_upgrader->bulk_upgrade( $language_updates );

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34747';
+$wp_version = '4.4-alpha-34748';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.