bug#21469: 25.0.50; right scrollbar wrongly placed when resizing split window

[martin rudalics]

> emacs -Q
> C-x 3 # split-window-right
> Then use the mouse to move the horizontal separator in the middle of
> the mode-line to the left. The frame stays the same size, but the
> right scrollbar moves inwards from the right edge. It also appears
> that the right scrollbar controls the window to the left, not the
> window to the right.
>
> This is with git emacs commit 166812addb0a1b9b2258ef3ce76424cd7facfa8b
>
> If I rebuild using ‘--without-toolkit-scroll-bars’ everything works as
> expected.
>
> In GNU Emacs 25.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.13)
>   of 2015-09-13
> Windowing system distributor 'The X.Org Foundation', version 11.0.11701000
> System Description:        Ubuntu 15.04
>
> Configured features:
> XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
> NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
> TOOLKIT_SCROLL_BARS GTK3 X11

I cannot reproduce that here with GTK+ 3.4.2.  Does it also happen when
you do (set-frame-parameter nil 'right-divider-width 6)?  Could this be
cairo related?

martin