@Override
    public HandlerRegistration addRangeChangeHandler(RangeChangeEvent.Handler handler) {
        return presenter.addRangeChangeHandler(handler);
    }
Add a {@link LoadingStateChangeEvent.Handler} to be notified of changes in
the loading state.

@param handler the handle
@return the registration for the handler
stroom-core-client-widget/src/main/java/com/google/gwt/user/cellview/client/AbstractHasData.java