AjaxBlock.php

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

class AjaxBlock extends \Magento\Backend\Controller\Adminhtml\Dashboard
{
    /**
     * @var \Magento\Framework\Controller\Result\RawFactory
     */
    protected $resultRawFactory;

    /**
     * @var \Magento\Framework\View\LayoutFactory
     */
    protected $layoutFactory;

    /**
     * @param \Magento\Backend\App\Action\Context $context
     * @param \Magento\Framework\Controller\Result\RawFactory $resultRawFactory
     * @param \Magento\Framework\View\LayoutFactory $layoutFactory
     */
    public function __construct(
        \Magento\Backend\App\Action\Context $context,
        \Magento\Framework\Controller\Result\RawFactory $resultRawFactory,
        \Magento\Framework\View\LayoutFactory $layoutFactory
    ) {
        parent::__construct($context);
        $this->resultRawFactory = $resultRawFactory;
        $this->layoutFactory = $layoutFactory;
    }

    /**
     * @return \Magento\Framework\Controller\Result\Raw
     */
    public function execute()
    {
        $output = '';
        $blockTab = $this->getRequest()->getParam('block');
        $blockClassSuffix = str_replace(
            ' ',
            '\\',
            ucwords(str_replace('_', ' ', $blockTab))
        );
        if (in_array($blockTab, ['tab_orders', 'tab_amounts', 'totals'])) {
            $output = $this->layoutFactory->create()
                ->createBlock('Magento\\Backend\\Block\\Dashboard\\' . $blockClassSuffix)
                ->toHtml();
        }
        /** @var \Magento\Framework\Controller\Result\Raw $resultRaw */
        $resultRaw = $this->resultRawFactory->create();
        return $resultRaw->setContents($output);
    }
}