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

chrome/browser/ui/libgtk2ui/gtk2_ui.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/ui/libgtk2ui/gtk2_ui.h"
 
 #include <set>
 
 #include <pango/pango.h>
 
@@ skipping 362 matching lines @@
     LOG(WARNING) << "Unexpected gtk-xft-rgba \"" << rgba << "\"";
     params.subpixel_rendering = gfx::FontRenderParams::SUBPIXEL_RENDERING_NONE;
   }
 
   g_free(hint_style);
   g_free(rgba);
 
   return params;
 }
 
-// Queries GTK for its font DPI setting and returns the number of pixels in a
-// point.
-double GetPixelsInPoint(float device_scale_factor) {
+double GetDPI() {
   GtkSettings* gtk_settings = gtk_settings_get_default();
   CHECK(gtk_settings);
   gint gtk_dpi = -1;
   g_object_get(gtk_settings, "gtk-xft-dpi", &gtk_dpi, NULL);
 
   // GTK multiplies the DPI by 1024 before storing it.
-  double dpi = (gtk_dpi > 0) ? gtk_dpi / 1024.0 : 96.0;
+  return (gtk_dpi > 0) ? gtk_dpi / 1024.0 : 96.0;
+}
+
+// Queries GTK for its font DPI setting and returns the number of pixels in a
+// point.
+double GetPixelsInPoint(float device_scale_factor) {
+  double dpi = GetDPI();
 
   // Take device_scale_factor into account — if Chrome already scales the
   // entire UI up by 2x, we should not also scale up.
   dpi /= device_scale_factor;
 
   // There are 72 points in an inch.
   return dpi / 72.0;
 }
 
 views::LinuxUI::NonClientMiddleClickAction GetDefaultMiddleClickAction() {
@@ skipping 1010 matching lines @@
   LoadGtkValues();
   NativeThemeGtk2::instance()->NotifyObservers();
 }
 
 void Gtk2UI::UpdateDeviceScaleFactor(float device_scale_factor) {
   device_scale_factor_ = device_scale_factor;
   GtkStyle* label_style = gtk_rc_get_style(fake_label_.get());
   UpdateDefaultFont(label_style->font_desc);
 }
 
+float Gtk2UI::GetDeviceScaleFactor() const {
+  const int kCSSDefaultDPI = 96;
+  const float scale = GetDPI() / kCSSDefaultDPI;
+  return ui::GetScaleForScaleFactor(ui::GetSupportedScaleFactor(scale));
+}
+
 }  // namespace libgtk2ui
 
 views::LinuxUI* BuildGtk2UI() {
   return new libgtk2ui::Gtk2UI;
 }