code: public function addSubscriber(EventSubscriberInterface $subscriber)
      {
          foreach ($subscriber->getSubscribedEvents() as $eventName => $params) {
              if (is_string($params)) {
                  $this->addListener($eventName, array($subscriber, $params));
              } elseif (is_string($params[0])) {
                  $this->addListener($eventName, array($subscriber, $params[0]), isset($params[1]) ? $params[1] : 0);
              } else {
                  foreach ($params as $listener) {
                      $this->addListener($eventName, array($subscriber, $listener[0]), isset($listener[1]) ? $listener[1] : 0);
                  }
              }
          }
      }
docs: Adds object methods as listeners for the events in getSubscribedEvents
  
  @see EventSubscriberInterface
  
  @param EventSubscriberInterface $subscriber