bug#22466: 25.0.50; disable-theme apparently forces a redisplay and causes a screen flash

[Eli Zaretskii]

> From: Artur Malabarba <bruce.connor.am@gmail.com>
> Cc: 22466@debbugs.gnu.org
> Date: Wed, 27 Jan 2016 20:20:43 +0000
> 
> > Then it would make sense to find a way of switching a theme without
> > changing the frame's background color, if that's possible (i.e. if the
> > new theme keeps the same background color).  If there's a function
> > missing for that, I'd suggest to add one.
> 
> How about just running that form only when necessary (i.e., only if the
> disabled theme actually sets the frame `background-color')?

Yes, something like that.  Or maybe add a new switch-theme API that
receives both the old and a new theme, and changes the background
color only if the new theme sets a different one.