bug#30699: 26.0.91; buffer contents flicker on macOS frames when frames are resized

[Eli Zaretskii]

> From: Aaron Jensen <aaronjensen@gmail.com>
> Date: Sun, 4 Mar 2018 23:55:50 -0800
> Cc: 30699@debbugs.gnu.org
> 
> It's a naive question, but is it at all possible to redraw a garbaged
> frame w/o a flicker?

AFAIK, no.  Redrawing a garbaged frame involves clearing it and
completely redrawing all of its windows, and that is what you perceive
as flicker.