Modifies the threshold for hidpi displays.

ash/display/display_change_observer_chromeos.h

 // Copyright 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 ASH_DISPLAY_DISPLAY_CHANGE_OBSERVER_CHROMEOS_H
 #define ASH_DISPLAY_DISPLAY_CHANGE_OBSERVER_CHROMEOS_H
 
 #include "ash/ash_export.h"
 #include "ash/shell_observer.h"
 #include "base/basictypes.h"
 #include "ui/display/chromeos/display_configurator.h"
 
 namespace ash {
 
 struct DisplayMode;
 
 // An object that observes changes in display configuration and
 // update DisplayManagers.
 class DisplayChangeObserver : public ui::DisplayConfigurator::StateController,
                               public ui::DisplayConfigurator::Observer,
                               public ShellObserver {
  public:
   // Returns the resolution list.
   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();
 
   // ui::DisplayConfigurator::StateController overrides:
   virtual ui::MultipleDisplayState GetStateForDisplayIds(
       const std::vector<int64>& outputs) const OVERRIDE;
   virtual bool GetResolutionForDisplayId(int64 display_id,
                                          gfx::Size* size) const OVERRIDE;
 
   // Overriden from ui::DisplayConfigurator::Observer:
   virtual void OnDisplayModeChanged(
       const ui::DisplayConfigurator::DisplayStateList& outputs) OVERRIDE;
 
   // Overriden from ShellObserver:
   virtual void OnAppTerminating() OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DisplayChangeObserver);
 };
 
 }  // namespace ash
 
 #endif  // ASH_DISPLAY_AURA_DISPLAY_CHANGE_OBSERVER_CHROMEOS_H