Add ServiceWorker.prototype.registration

[annevk]

Would be kind of convenient to have a pointer to a ServiceWorker's corresponding ServiceWorkerRegistration instance. Or is it too problematic that you can then get to it synchronously from the controller?

[wanderview]

Even if its async, it would be nice to conclusively get the registration managing the ServiceWorker object. Currently things like getRegistration() could conceivably give you a different registration.

[jakearchibald]

Not against adding this unless the synchronous nature (or circular reference) is problematic.