title: Alerting website visitors that a chrome extension is available - how?
body: <p>The <a href="http://www.independent.co.uk" rel="nofollow noreferrer">Independent website</a> has a little widget that pops up a message informing you that there is an Independent Chrome extension available when you visit it using Chrome (v7 in my case): </p>
  
  <p><img src="https://i.stack.imgur.com/wJw4z.jpg" alt=" "></p>
  
  <p>Is this part of the Chrome extensions API - if so how is it achieved (or have they custom-rolled their own JavaScript to make it look like part of Chrome)? A quick look at the source of the page revealed nothing obvious.</p>