Button distroy = new Button("time the removal", new ClickHandler() {
public void onClick(ClickEvent event) {
Duration d = new Duration();
target.clear();
log.report("Took " + d.elapsedMillis() + " milliseconds to clear "
+ size.getValue() + " widgets from a flow panel");
for (Widget child : children) {
if (child.getElement().getPropertyString("__listener") != null) {
throw new IllegalStateException(
"each child should no longer have a listener");