Because the WP_ADMIN constant name can be bound in multiple files, all instances should check ! defined first. wp-admin/admin.php already has this check.

See #27881.


git-svn-id: https://develop.svn.wordpress.org/trunk@28478 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/admin-ajax.php

@@ -14,7 +14,9 @@
  * @since 2.1.0
  */
 define( 'DOING_AJAX', true );
-define( 'WP_ADMIN', true );
+if ( ! defined( 'WP_ADMIN' ) ) {
+	define( 'WP_ADMIN', true );
+}
 
 /** Load WordPress Bootstrap */
 require_once( dirname( dirname( __FILE__ ) ) . '/wp-load.php' );