protected function validateCartItemCheckout($sku, $item)
    {
        $item += array(
            'sku' => $sku,
            'increment' => false,
            'admin' => !empty($this->admin),
            'user_id' => $this->order_user_id,
            'store_id' => $this->order_store_id
        );

        $this->setSubmitted('update', $item);
        $this->setSubmitted("cart.items.$sku", $item);

        return $this->validateComponent('cart', array('parents' => "cart.items.$sku"));
    }