title: How to build an chrome extension like Google Hangouts
body: <p>The <a href="https://chrome.google.com/webstore/detail/nckgahadagoaajjgafhacjanaoiihapd" rel="noreferrer">Google Hangouts extension</a> has a panel that shows up outside of the Chrome UI.</p>
  
  <p>It is sort of like a notification but not. I don't see anything in the Extension Developer Docs that describes an API to make this work. Is this a Google-specific hack they're doing? Is there something in the experimental APIs that I'm missing?</p>