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

[Eli Zaretskii]

> Date: Tue, 13 Mar 2018 12:19:04 +0000
> From: Alan Third <alan@idiocy.org>
> Cc: 30699@debbugs.gnu.org, aaronjensen@gmail.com
> 
> I think the only solution left is to take a copy of the contents of
> the frame, resize, then copy the contents back. I don’t know how to do
> that and a quick google search reveals nothing helpful.

What about the idea I brought up earlier: to avoid blanking the frame
in this case (but still mark it garbaged)?