Constructs a new scroll handler with a custom scroll threshold.
The scroll threshold is the distance from the bottom edge of the scrolled content
such that when the distance from the bottom edge of the scroll viewport to the bottom
edge of the scrolled content becomes lower than the distance, the scroll action is triggered.
public void onScroll(com.google.gwt.event.dom.client.ScrollEvent event)
onScroll in interface com.google.gwt.event.dom.client.ScrollHandler