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

chrome/browser/ui/libgtk2ui/gtk2_ui.cc

Index: chrome/browser/ui/libgtk2ui/gtk2_ui.cc
diff --git a/chrome/browser/ui/libgtk2ui/gtk2_ui.cc b/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
index 2f7f2cd93cfb7e6629ebaa96c8f8b5012a4cea20..a57b59fb7905762f861446e6587b52f536adf2dc 100644
--- a/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
+++ b/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
@@ -380,16 +380,20 @@ gfx::FontRenderParams GetGtkFontRenderParams() {
   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.
@@ -1420,6 +1424,12 @@ void Gtk2UI::UpdateDeviceScaleFactor(float device_scale_factor) {
   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() {