Instead of passing through window's associated document's URL as
an extra argument to starting up a worker. This will allow for
improving the representation of 'outside settings' when setting
up a Worker.
This is required to store Content Security Policies, as their
Directives are implemented as subclasses with overridden virtual
functions. Thus, they cannot be stored as generic Directive classes, as
it'll lose the ability to call overridden functions when they are
copied.
