Symfony\Component\HttpFoundation\Response::mustRevalidate PHP Метод

    public function mustRevalidate()
    {
        return $this->headers->hasCacheControlDirective('must-revalidate') || $this->headers->hasCacheControlDirective('proxy-revalidate');
    }

 public function track(Request $request)
 {
     $this->request = $request;
     $referer = $this->request->query->get('utmr', '');
     $path = $this->request->query->get('utmp', '');
     $account = $this->request->query->get('utmac');
     $userAgent = $this->request->server->get('HTTP_USER_AGENT', '');
     $visitorId = $this->request->cookies->get($this->cookieName);
     if (empty($visitorId)) {
         $visitorId = $this->getVisitorId($this->getGuidHeader(), $account, $userAgent);
     }
     $url = $this->constructGifUrl($referer, $path, $account, $visitorId, $this->maskVisitorIp());
     $this->browser->get($url, array('Accept-Language: ' . $this->request->server->get('HTTP_ACCEPT_LANGUAGE'), 'User-Agent: ' . $userAgent));
     $cookie = new Cookie($this->cookieName, $visitorId, time() + $this->cookiePersistence, $this->cookiePath, $this->request->getHost());
     $response = new Response();
     $response->headers->add(array('Content-Type' => 'image/gif', 'Pragma' => 'no-cache'));
     $response->setPrivate();
     $response->mustRevalidate();
     $response->setExpires(new \DateTime('-10 year'));
     $response->setContent(join($this->gifData));
     $response->headers->setCookie($cookie);
     return $response;
 }