Registers a ServiceWorker with script loaded from aScriptURI
to act as
the ServiceWorker for aScope. Requires a valid entry settings object on
the stack. This means you must call this from content code ‘within’
a window.
Returns a Promise.
Unregister an existing ServiceWorker registration for aScope
.
It keeps aCallback alive until the operation is concluded.
Call this to request that document aDoc
be controlled by a ServiceWorker
if a registration exists for it’s scope.
This MUST only be called once per document!
Documents that have called MaybeStartControlling() should call this when
they are destroyed. This function may be called multiple times, and is
idempotent.