Preparing a WPTest...

I'm not sure this is Web compatible -

1. subscribe() can be called from within a service worker, where there are no local activations that can be consumed -- particularly the consume user activation steps assume that there's a window.
2. Looking at our metrics, only about a fourth of permission requests happen with a gesture. We mitigate against this by displaying a different user interface (if any at all) in those cases. In my reading it would be valid for an implementation not to show any prompt at all.

Note that Gecko opted to require user activation only if the permission is not granted, and just proceeds without activation if it's granted, which I think is the best way as reportedly some websites repeatedly calls pushManager.subscribe() every time: https://bugzilla.mozilla.org/show_bug.cgi?id=1486010#c5

Instead, the page calls pushManager.subscribe every time you visit it

I'll take a closer look at what WebKit does... we might be doing something similar @saschanaz.