1. protected
void stopTrackingIfPointerNoLongerDown(PointerEvent event)

Stops tracking the pointer associated with the given event if the event is a PointerUpEvent or a PointerCancelEvent event.

Source 

@protected
void stopTrackingIfPointerNoLongerDown(PointerEvent event) {
  if (event is PointerUpEvent || event is PointerCancelEvent)
    stopTrackingPointer(event.pointer);
}