device scale factor detection: use gtk-xft-dpi consistently

chrome/browser/ui/libgtk2ui/gtk2_ui.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_UI_LIBGTK2UI_GTK2_UI_H_
 #define CHROME_BROWSER_UI_LIBGTK2UI_GTK2_UI_H_
 
 #include <map>
 #include <vector>
 
@@ skipping 103 matching lines @@
   bool UnityIsRunning() override;
   NonClientMiddleClickAction GetNonClientMiddleClickAction() override;
   void NotifyWindowManagerStartupComplete() override;
 
   // ui::TextEditKeybindingDelegate:
   bool MatchEvent(const ui::Event& event,
                   std::vector<ui::TextEditCommandAuraLinux>* commands) override;
 
   // ui::Views::LinuxUI:
   void UpdateDeviceScaleFactor(float device_scale_factor) override;
+  float GetDeviceScaleFactor() const override;
 
  private:
   typedef std::map<int, SkColor> ColorMap;
   typedef std::map<int, color_utils::HSL> TintMap;
   typedef std::map<int, gfx::Image> ImageCache;
 
   // This method returns the colors webkit will use for the scrollbars. When no
   // colors are specified by the GTK+ theme, this function averages of the
   // thumb part and of the track colors.
   void GetScrollbarColors(GdkColor* thumb_active_color,
@@ skipping 140 matching lines @@
 }  // namespace libgtk2ui
 
 // Access point to the GTK2 desktop system. This should be the only symbol that
 // is exported in the library; everything else should be used through the
 // interface, because eventually this .so will be loaded through dlopen at
 // runtime so our main binary can conditionally load GTK2 or GTK3 or EFL or
 // QT or whatever.
 LIBGTK2UI_EXPORT views::LinuxUI* BuildGtk2UI();
 
 #endif  // CHROME_BROWSER_UI_LIBGTK2UI_GTK2_UI_H_