Note that as of this commit, there aren't any such throwers, and the
call site in Heap::allocate will drop exceptions on the floor. This
commit only serves to change the declaration of the overrides, make sure
they return an empty value, and to propagate OOM errors frm their base
initialize invocations.
This needs to happen before prototype/constructor intitialization can be
made lazy. Otherwise, GC could run during the C++ constructor and try to
collect the object currently being created.
Get rid of the bespoke NavigatorObject class and use the modern IDL
strategies for creating platform objects to re-implement Navigator and
its associcated mixin interfaces. While we're here, implement it in a
way that brings WorkerNavigator up to spec :^)
