Sets the scrollbar policy for the horizontal and vertical scrollbars.
The policy determines when the scrollbar should appear; it is a value from the GtkPolicyType enumeration. If Gtk::POLICY_ALWAYS, the scrollbar is always present; if Gtk::POLICY_NEVER, the scrollbar is never present; if Gtk::POLICY_AUTOMATIC, the scrollbar is present only if needed (that is, if the slider part of the bar would be smaller than the trough - the display is larger than the page size).
See also: get_policy()