UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36

Steps to reproduce the problem:
1. Visit this [demo page](https://mdn.mozillademos.org/en-US/docs/Web/API/Notifications_API/Using_the_Notifications_API$samples/Tag_example?revision=1393671) (referenced in this [MDN article](https://developer.mozilla.org/en-US/docs/Web/API/Notifications_API/Using_the_Notifications_API#Tag_example))
2. Allow notifications for the page
3. Click Notify Me

What is the expected behavior?
Because multiple desktop notifications are triggered in succession with the same "tag" attribute, the active notification should be replaced by each subsequent one. 

This is the behaviour in both Safari and Firefox

What went wrong?
Only the first one is shown.

Did this work before? N/A 

Does this work in other browsers? N/A

Chrome version: 71.0.3578.98  Channel: stable
OS Version: OS X 10.14.0
Flash Version: 

From [MDN](https://developer.mozilla.org/en-US/docs/Web/API/Notifications_API/Using_the_Notifications_API#Tag_example):

> If a notification already has the same tag and has not been displayed yet, the new notification replaces that previous notification. If the notification with the same tag has already been displayed, the previous notification is closed and the new one is displayed.

From [Google Developer Docs](https://developers.google.com/web/fundamentals/push-notifications/notification-behaviour#tag): 

>Now let's show a third notification but re-use the first tag of 'message-group-1'. Doing this will close the first notification and replace it with our new notification.