title: How determine if the popup page is open or not?
body: <p>I'm working on a Chrome extension and I'm looking how to find out (from the background page) if the popup page is open or not. I looked into <a href="http://code.google.com/chrome/extensions/messaging.html" rel="noreferrer">message passing</a> but I'm not sure if that's gonna help me at this or if there's a simpler way.</p>
  
  <p>Thanks!</p>