code: protected <H extends EventHandler> HandlerRegistration addHandler(final H handler, GwtEvent.Type<H> type) {
  
          return ensureHandlers().addHandlerToSource(type, this, handler);
      }
docs: Adds this handler to the widget.
  
  @param <H> the type of handler to add
  @param type the event type
  @param handler the handler
  @return {@link HandlerRegistration} used to remove the handler