title: Adding resize listener/handler to VerticalPanel in GWT
body: <p>How do I add a listener/handler to a VerticalPanel such that it is
  triggered when the VerticalPanel changes in size?</p>
  
  <p>I've basically tried the following:</p>
  
  <pre><code>VerticalPanel myPanel = new VerticalPanel();
  //... code to add child widgets that may change the size of the parent vertical panel ...
  
  myPanel.addHandler(new ResizeHandler() {
    public void onResize(final ResizeEvent event) {
      //... code to handle resize of vertical panel ...
    }
  
  }, ResizeEvent.getType() );
  </code></pre>
  
  <p>but the handler doesn't get triggered. </p>