Hi!  I think maybe there's a bug in org-save-outline-visibility, or else I
misunderstand what that macro is supposed to do.  Test case:

1. Start Emacs 26.0.91 with -Q and load org-mode from master
(release_9.1.6-419-g4b2006).

2. Make an org-mode buffer with contents:

~~~~~~
* Foo
  :PROPERTIES:
  :bar:      baz
  :END:
~~~~~~

3. Fold the PROPERTIES drawer by moving to the line with :PROPERTIES: and
hitting TAB.

4. M-: (org-save-outline-visibility t (org-show-all)) RET

Expected result: PROPERTIES drawer is still folded

Observed result: PROPERTIES drawer is no longer folded, its contents have
become visible

Should org-save-outline-visibility save the visibility of drawers along
with other visibility?

I am wondering if this is perhaps a consequence of 4403d4685e19, "Give
drawers their own invisibility spec", where the 'org-hide-drawer
invisibility spec was introduced?  As a consequence,
org-outline-overlay-data (called by org-save-outline-visibility) no longer
saves the invisible overlays for drawers, since those overlays' 'invisible
property is no longer 'outline, but instead 'org-hide-drawer.

Thanks,
Dale