I've been using the `swRegistration.sync.register('tag')` API in an app I'm building. Unfortunately, once a sync has been registered, it's difficult to test.

This is a feature request to:

1) Allow me to force a sync event to fire, with provided tag, when some gesture is made in the DevTools.
2) Not as necessary, but still nice to have, show a list of the currently registered sync tags.

Currently, I have to kind of wait around for the sync event to fire, which is often quick (after re-enabling my network adapter, the only way to *really* go offline), but sometimes it is not. This makes testing painful at times.

If there is a better way to go about doing this, please let me know. I was unable to find a better way after asking around on Twitter: https://twitter.com/nikmd23/status/766849969303150592

Thanks,
Nik