bug#27647: 26.0.50; Line numbers implemented natively disappear momentarily when frame out of focus

[Eli Zaretskii]

> From: Kaushal Modi <kaushal.modi@gmail.com>
> Date: Tue, 17 Oct 2017 15:13:01 +0000
> Cc: 27647@debbugs.gnu.org, Eli Zaretskii <eliz@gnu.org>, 
> jonaswestlund101@gmail.com, 
>       npostavs@users.sourceforge.net, rom.skiad@gmail.com
> 
> Again, this problem happens only when x-gtk-use-system-tooltips is set to t.

So somehow, popping up and/or down the GTK tooltip causes a redisplay
cycle with display-line-numbers disabled.  If someone with a GTK build
can catch such a redisplay in a debugger and show a backtrace, that
would probably allow us to move forward.

Thanks.