Modifies the threshold for hidpi displays.

ash/display/display_change_observer_chromeos.h

Index: ash/display/display_change_observer_chromeos.h
diff --git a/ash/display/display_change_observer_chromeos.h b/ash/display/display_change_observer_chromeos.h
index 1e6521ff7816bf34e089e81015c241af384c7924..96740cfbba0cdee71dda9a927a086d1c8db61716 100644
--- a/ash/display/display_change_observer_chromeos.h
+++ b/ash/display/display_change_observer_chromeos.h
@@ -24,6 +24,11 @@ class DisplayChangeObserver : public ui::DisplayConfigurator::StateController,
   ASH_EXPORT static std::vector<DisplayMode> GetDisplayModeList(
       const ui::DisplayConfigurator::DisplayState& output);
 
+  // Returns the device scale factor for the specific monitor and mode.
+  ASH_EXPORT static float GetScaleFactor(
+      const gfx::Size& physical_size,
+      const gfx::Size& screen_size);
+
   DisplayChangeObserver();
   virtual ~DisplayChangeObserver();