[Deprecated in Chrome 44, removed in Chrome 45] We asked developers to indicate their intent to only send push messages that result in user visible UI - Web Notifications, by including the "gcm_user_visible_only" key in their Manifest. We are now removing this key in favor of the specified solution: userVisibleOnly. The subscribe() method should be updated like this: serviceWorkerRegistration.pushManager.subscribe({ userVisibleOnly: true }).then(...)
Docs: https://developer.mozilla.org/en-US/docs/Web/API/PushManager/subscribe http://updates.html5rocks.com/2015/05/Notifying-you-of-notificiation-changes
Samples: https://github.com/GoogleChrome/samples/tree/gh-pages/push-messaging-and-notifications