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 144 matching lines @@
 
   // Registers the overscan insets for the display of the specified ID. Note
   // that the insets size should be specified in DIP size. It also triggers the
   // display's bounds change.
   void SetOverscanInsets(int64 display_id, const gfx::Insets& insets_in_dip);
 
   // Sets the display's rotation.
   void SetDisplayRotation(int64 display_id, gfx::Display::Rotation rotation);
 
   // Sets the display's ui scale.
+  // TODO(mukai): remove this and merge into SetDisplayMode.
   void SetDisplayUIScale(int64 display_id, float ui_scale);
 
   // Sets the display's resolution.
+  // TODO(mukai): remove this and merge into SetDisplayMode.
   void SetDisplayResolution(int64 display_id, const gfx::Size& resolution);
 
+  // Sets the external display's configuration, including resolution change,
+  // ui-scale change, and device scale factor change.
+  void SetDisplayMode(int64 display_id, const DisplayMode& display_mode);
+
   // 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_