public void addMarkerManagerChangedHandler(
final MarkerManagerChangedHandler handler) {
maybeInitMarkerManagerChangedHandlers();
markerManagerChangedHandlers.addHandler(handler,
new LatLngBoundsIntCallback() {
@Override
public void callback(LatLngBounds bounds, int markerCount) {
MarkerManagerChangedEvent e = new MarkerManagerChangedEvent(
MarkerManager.this, bounds, markerCount);
handler.onChanged(e);