title: TTL feature not working on google chrome push notification
body: <p>I am using GCM to send push notifications to chrome and facing some of the problems as follows. I am using nodejs library web-push to send push.</p>
  
  <p>1) I am setting TTL key with value 0 of sendNotifiation of web-push and sending a notification while my browser is offline. And I opened my browser after a minute. Still I am getting the notification. I tried sending by curl request as well setting TTL header, still the same problem. As per doc, if TTL header is set to 0 and if end user is offline, He shouldn't get a notifcation. 
  <a href="https://www.npmjs.com/package/web-push" rel="nofollow">https://www.npmjs.com/package/web-push</a></p>
  
  <p>2) There is an option for timestamp key while showing notifications which will modify the timestamp on android chrome while reorder on desktop chrome. still time is not getting changed on android chrome even setting this field. <a href="https://developers.google.com/web/updates/2016/03/notifications?hl=en" rel="nofollow">https://developers.google.com/web/updates/2016/03/notifications?hl=en</a></p>
  
  <p>Thanks in advance.</p>