title: How do I get a GWT menu popup to stay within the browser window?
body: <p>My GWT app uses a DockLayoutPanel for primary layout and the page itself does not scroll. I have a PopupPanel with a MenuBar and sometimes when a MenuItem is selected the sub menu bar goes off the bottom of the screen abruptly forcing a new scroll bar into the browser and messing up the layout.</p>
  
  <p>How do I get the menu popup to behave nicely and reposition itself upward when the default positioning would put it out of the browser viewport (the way that PopupPanel.showRelativeTo(uiTarget) positioning works)?</p>
  
  <p>In looking at the MenuBar source, it looks like all the layout is done in private methods, so I can't fix it in subclass, and I don't see any events I can listen to that would allow me to do the repositioning myself.</p>