public function __construct(Tracker $tracker, EventManager $event_manager, Tracker_IDisplayTrackerLayout $layout)
{
parent::__construct($tracker, $event_manager);
$this->layout = $layout;
}
public function __construct(Tracker $tracker, Tracker_Artifact $source_artifact, EventManager $event_manager, Tracker_IFetchTrackerSwitcher $tracker_switcher)
{
parent::__construct($tracker, $event_manager);
$this->source_artifact = $source_artifact;
$this->tracker_switcher = $tracker_switcher;
}