[gnome-tweak-tool/scaling] add tweak for Gdk/WindowScalingFactor

[John Stowers <jstowers src gnome org>]

commit e1c22bbfe294e8a53adbbcf084594761c88fcbdf
Author: John Stowers <john stowers gmail com>
Date:   Wed Mar 26 21:09:08 2014 +0100

    add tweak for Gdk/WindowScalingFactor

 gtweak/tweaks/tweak_group_windows.py |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/gtweak/tweaks/tweak_group_windows.py b/gtweak/tweaks/tweak_group_windows.py
index a888b57..9e559fb 100644
--- a/gtweak/tweaks/tweak_group_windows.py
+++ b/gtweak/tweaks/tweak_group_windows.py
@@ -21,6 +21,8 @@ from gtweak.tweakmodel import TWEAK_GROUP_WINDOWS, Tweak
 from gtweak.widgets import ListBoxTweakGroup, GSettingsComboEnumTweak, GSettingsComboTweak, 
GSettingsSwitchTweak, Title, GSettingsSwitchTweakValue, build_label_beside_widget
 from gtweak.utils import XSettingsOverrides
 
+from gi.repository import Gtk
+
 _shell = GnomeShellFactory().get_shell()
 _shell_loaded = _shell is not None