bug#20432: GDK_SCALE=2 GDK_DPI_SCALE=0.5 destroys GTK+ 3 scroll bar

["Felix E. Klee" <felix.klee@inka.de>]

I'm running Emacs on high DPI screen, and for scaling icons and other UI
elements in GTK+ applications, I've set in the environment:

    GDK_SCALE=2
    GDK_DPI_SCALE=0.5

This, however, confuses EMACS: The scrollbar gets squished.



In GNU Emacs 24.5.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.2)
 of 2015-04-20 on bitzer.hoetzel.info
Windowing system distributor `The X.Org Foundation', version 11.0.11701000
System Description: Arch Linux

Configured using:
 `configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong
 --param=ssp-buffer-size=4' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...
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scroll-up-command: End of buffer

Load-path shadows:
None found.

Features:
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Memory information:
((conses 16 74597 8753)
 (symbols 48 17662 0)
 (miscs 40 64 138)
 (strings 32 9283 4419)
 (string-bytes 1 253558)
 (vectors 16 8988)
 (vector-slots 8 384078 17367)
 (floats 8 64 222)
 (intervals 56 183 16)
 (buffers 960 13)
 (heap 1024 24992 889))