Toggle desktop saving (Desktop Save mode).
With a prefix argument ARG, enable Desktop Save mode if ARG is
positive, and disable it otherwise. If called from Lisp, enable
the mode if ARG is omitted or nil.
If Desktop Save mode is enabled, the state of Emacs is saved from
one session to another. See variable `desktop-save' and function
`desktop-read' for details.
(fn &optional ARG)
Non-nil if Desktop-Save mode is enabled.
See the command `desktop-save-mode' for a description of this minor mode.