Clear Registration should call Update Registration State before Update Worker State

[wanderview]

We have two different algorithms for updating DOM objects on their various javascript threads:

• Update Worker State sets the DOM object's .state value and fires a statechange event.
• Update Registration State sets the DOM object's .installing, .waiting, and .active properties. It does not fire an event.

Both of these algorithms independently queue tasks to do the DOM object modifications.

In nearly all cases in the spec Update Registration State occurs before Update Worker State. This is good because it means the registration DOM objects will be in a consistent state the statechange event fires.

The Clear Registration algorithm, though, does things in the reverse order. It calls Update Worker State for moving each worker to the redundant state. It then calls Update Registration State afterwards to clear its reference on the registration DOM object.

I think this is wrong because it means the statechange event to redundant will fire while the worker is still visible on the registration.

[wanderview]

Close in favor of #1273.