[Form] Add a missing property delcaration in the ResizeFormListener

src/Symfony/Component/Form/Extension/Core/EventListener/ResizeFormListener.php

@@ -36,10 +36,17 @@ class ResizeFormListener implements EventSubscriberInterface
     private $type;
 
     /**
+     * Whether children could be added to the group
      * @var Boolean
      */
     private $allowAdd;
 
+    /**
+     * Whether children could be removed from the group
+     * @var Boolean
+     */
+    private $allowDelete;
+
     public function __construct(FormFactoryInterface $factory, $type, $allowAdd = false, $allowDelete = false)
     {
         $this->factory = $factory;