magento2/app/code/Magento/Backend/Controller/Adminhtml/Cache/CleanMedia.php

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

use Magento\Framework\App\Action\HttpGetActionInterface as HttpGetActionInterface;
use Magento\Framework\Exception\LocalizedException;
use Magento\Framework\Controller\ResultFactory;

class CleanMedia extends \Magento\Backend\Controller\Adminhtml\Cache implements HttpGetActionInterface
{
    /**
     * Authorization level of a basic admin session
     *
     * @see _isAllowed()
     */
    const ADMIN_RESOURCE = 'Magento_Backend::flush_js_css';

    /**
     * Clean JS/css files cache
     *
     * @return \Magento\Backend\Model\View\Result\Redirect
     */
    public function execute()
    {
        try {
            $this->_objectManager->get(\Magento\Framework\View\Asset\MergeService::class)->cleanMergedJsCss();
            $this->_eventManager->dispatch('clean_media_cache_after');
            $this->messageManager->addSuccessMessage(__('The JavaScript/CSS cache has been cleaned.'));
        } catch (LocalizedException $e) {
            $this->messageManager->addErrorMessage($e->getMessage());
        } catch (\Exception $e) {
            $this->messageManager
                ->addExceptionMessage($e, __('An error occurred while clearing the JavaScript/CSS cache.'));
        }

        /** @var \Magento\Backend\Model\View\Result\Redirect $resultRedirect */
        $resultRedirect = $this->resultFactory->create(ResultFactory::TYPE_REDIRECT);
        return $resultRedirect->setPath('adminhtml/*');
    }
}