src/TrackerFactory.php
public function buildTracker($numItems = Tracker::UNKNOWN, array $extraSubscribers = [])
    {
        $tracker = new Tracker($numItems);

        foreach (array_merge($this->defaultSubscribers, $extraSubscribers) as $listener) {
            $tracker->getDispatcher()->addSubscriber($listener);
        }

        return $tracker;
    }
public function buildTracker($numItems = Tracker::UNKNOWN, array $extraSubscribers = [])
    {
        $tracker = new Tracker($numItems);

        foreach (array_merge($this->defaultSubscribers, $extraSubscribers) as $listener) {
            $tracker->getDispatcher()->addSubscriber($listener);
        }

        return $tracker;
    }
Build a new Tracker instance

If $extraSubscribers is not empty, those subscribers will be added
to the Tracker in addition to the defaults.

@param int                               $numItems          The total number of items (or -1 for unknown)
@param array|EventSubscriberInterface[]  $extraSubscribers  Optionally specify extra listeners for this Tracker instance
@return Tracker