magento2/app/code/Magento/Newsletter/Controller/Adminhtml/Subscriber.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Newsletter\Controller\Adminhtml;

/**
 * Newsletter subscribers controller
 */
abstract class Subscriber extends \Magento\Backend\App\Action
{
    /**
     * Authorization level of a basic admin session
     *
     * @see _isAllowed()
     */
    const ADMIN_RESOURCE = 'Magento_Newsletter::subscriber';

    /**
     * @var \Magento\Framework\App\Response\Http\FileFactory
     */
    protected $_fileFactory;

    /**
     * @param \Magento\Backend\App\Action\Context $context
     * @param \Magento\Framework\App\Response\Http\FileFactory $fileFactory
     */
    public function __construct(
        \Magento\Backend\App\Action\Context $context,
        \Magento\Framework\App\Response\Http\FileFactory $fileFactory
    ) {
        $this->_fileFactory = $fileFactory;
        parent::__construct($context);
    }
}