Introduce user customization of external HighDPI mode for 4K monitor.

ash/display/display_manager.h

 // 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.
 
 #ifndef ASH_DISPLAY_DISPLAY_MANAGER_H_
 #define ASH_DISPLAY_DISPLAY_MANAGER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 64 matching lines @@
   //    recognized as a part of desktop.
   enum SecondDisplayMode {
     EXTENDED,
     MIRRORING,
     VIRTUAL_KEYBOARD
   };
 
   // Returns the list of possible UI scales for the display.
   static std::vector<float> GetScalesForDisplay(const DisplayInfo& info);
 
+  // Returns the list of possible device scale factors for the external display.
+  static std::vector<float> GetDeviceScaleFactorsForDisplay(
+      const DisplayInfo& info);
+
   // Returns next valid UI scale.
   static float GetNextUIScale(const DisplayInfo& info, bool up);
 
   // Updates the bounds of the display given by |secondary_display_id|
   // according to |layout|.
   static void UpdateDisplayBoundsForLayoutById(
       const DisplayLayout& layout,
       const gfx::Display& primary_display,
       int64 secondary_display_id);
 
@@ skipping 65 matching lines @@
 
   // Sets the display's rotation.
   void SetDisplayRotation(int64 display_id, gfx::Display::Rotation rotation);
 
   // Sets the display's ui scale.
   void SetDisplayUIScale(int64 display_id, float ui_scale);
 
   // Sets the display's resolution.
   void SetDisplayResolution(int64 display_id, const gfx::Size& resolution);
 
+  // Sets the external display's device scale factor.
+  void SetDisplayDeviceScaleFactor(int64 display_id, float device_scale_factor);
+
   // Register per display properties. |overscan_insets| is NULL if
   // the display has no custom overscan insets.
   void RegisterDisplayProperty(int64 display_id,
                                gfx::Display::Rotation rotation,
                                float ui_scale,
                                const gfx::Insets* overscan_insets,
                                const gfx::Size& resolution_in_pixels,
                                ui::ColorCalibrationProfile color_profile);
 
   // Returns the display's selected mode.
@@ skipping 181 matching lines @@
   SecondDisplayMode second_display_mode_;
   int64 mirrored_display_id_;
   gfx::Display non_desktop_display_;
 
   DISALLOW_COPY_AND_ASSIGN(DisplayManager);
 };
 
 }  // namespace ash
 
 #endif  // ASH_DISPLAY_DISPLAY_MANAGER_H_