title: Getting cross device notification dismissal working with Device Group Messaging
body: <p>In the docs for Device Group Messaging it says that deleting a notification on one device deletes it on all the others.
  How do I implement this? I don't see any way to map a GCM push to a notification.</p>
  
  <p>"If a message has been handled on one device, the GCM message on the other devices are dismissed. For example, if a user has handled a calendar notification on a watch the notification will go away on the user's phone and tablet."</p>
  
  <p><a href="https://developers.google.com/cloud-messaging/notifications" rel="nofollow">https://developers.google.com/cloud-messaging/notifications</a></p>