What happens if ...?

When do we get an unsubscription event from Google?

Clearing Cookies and other site and plugin data after subscribing, and sending another message

Environment: Chrome 54.0.2840.87 (64-bit) on Mac OS X 10.11.6

Revision: c5ec6c5a12f2ed748bb08c1a8567b3c0df89dccd-refs/branch-heads/2840@{#805}

1. Subscribe.
2. Close the tab you subscribed on.
3. Clear Cookies and other site and plugin data (Settings -> Privacy -> Clear Browsing Data...).
4. Send yourself a notification.
5. Observe delivery results are okay.
6. Send yourself another notification.
7. Observe delivery results mark you as unsubscribed.

Do we get a unsubscription event right after the first message delivery?

No. It looks like the browser sends an unregistration message though:

Do we get an unsubscription event right after the second message delivery?

Yes. Google immediately tells us the user is no longer subscribed. The browser's chrome://gcm-internals does not record any message received.

Note: It looks like clearing Cookies and other site and plugin data is the only setting necessary in clearing browser data to unsubscribe the user (all the other clearing options are unrelated).