button.addMouseMoveHandler(new MouseMoveHandler() {
public void onMouseMove(MouseMoveEvent event) {
passTest(event.getNativeEvent());
}
});
button.addMouseOutHandler(new MouseOutHandler() {
public void onMouseOut(MouseOutEvent event) {
NativeEvent nativeEvent = event.getNativeEvent();
assert nativeEvent.getRelatedEventTarget() != null;
assert nativeEvent.getEventTarget() != null;
if (button.getElement().equals(nativeEvent.getEventTarget())