title: Google+ interactive post - How to add callbacks for buttons?
body: <p>I'm using the <a href="https://developers.google.com/+/web/share/interactive" rel="nofollow">Google+ interactive post</a> feature where the posting window offers a <code>close</code> and <code>share</code> button.
  How can I detect which one the user clicked? I can't find callbacks in their <a href="https://developers.google.com/+/web/share/interactive#javascript_api" rel="nofollow">JavaScript API</a> - is it possible to add <em>custom ones</em>?    </p>