title: Getting customized message from GCM using Web push notifications
body: <p>I'm using Web push notifications with Chrome, and they work great. But now I want to deliver a custom message in my notifications.  I can have my Service Worker call out to my site to get content, as is done at <a href="https://simple-push-demo.appspot.com/" rel="nofollow">https://simple-push-demo.appspot.com/</a>—which is fine if I want every recipient to see the same message. </p>
  
  <p>Is there any way to get either the recipient’s <code>registration_id</code> or the <code>message_id</code> that GCM returns? If I could get either of these and include them in the callback to the service, I could customize the response.</p>
  
  <p>Also, any info on when we might be able to include a payload in the call to GCM?</p>