title: How to center a popup/dialog window in GWT?
body: <p>I have a list of records, each record has a button that opens setting window. Also I have preferences with a lot of logical parts and each part has some records with a button.</p>
  
  <p>So, when I click on a button, dialog window appears, but if this button is somewhere in the bottom the page (let it be 300 records with button), my dialog window appears on the top. As a result I have to scroll up in order to find this window (sometimes it appears behind browser borders).</p>
  
  <p>Or just imagine that you configure something and scroll page down filling each option, at the end you saves your configuration but some fields were filled incorrectly and warning popup window appears... somewhere on page, but not near your pointer or even not in the middle of your current page.</p>
  
  <p>All my dialog windows are inherited from DialogBox, so I use super.show() and super.center(), but it doesn't work as I want it to.</p>
  
  <p>Small info addition: some dialog windows receive data from server and when all the data is received the rest of the window is displayed. I suspect this can cause sometimes window to appear in a wrong place.</p>