Add restart UI

[muffinresearch]

Fixes mozilla/addons#9681

The UNINSTALLING restart case only occurs if someone clicks remove from about:addons#Extensions. Handling the user clicking undo is covered by mozilla/addons#9693.

Both kinds of restart look like this:

[coveralls]

Coverage remained the same at 100.0% when pulling bfc6be9 on muffinresearch:restart-ui into 56cd0c5 on mozilla:master.

[mstriemer]

Will webpack inline these or do they need to be required?

[muffinresearch]

Yeah it should inline it automagically since it's tiny.

[mstriemer]

Do we see the needsRestart state on a reload? Should you be able to close the UNINSTALLING notice? You could presumably uninstall by accident and want to install again.

r+wc

[muffinresearch]

Do we see the needsRestart state on a reload?

No, since we don't get that hint from the introspection. I'm not sure if that would be an issue or not.

Should you be able to close the UNINSTALLING notice? You could presumably uninstall by accident and want to install again.

It's possible we could have an undo instead of close, since the unstalling state is still pending. It'll certainly be worth looking at that separately. I'll file a new issue to cover that. Maybe 'undo' could work for all restart cases?

[mstriemer]

If it is needsRestart then the state should be INSTALLING or UNINSTALLING, right? I think we could just do the opposite in the case of an undo, good call.