Remember the configured device scale factor for external displays.

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 164 matching lines @@
   // case the new resolution actually doesn't work.
   bool 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,
+                               float device_scale_factor,
                                ui::ColorCalibrationProfile color_profile);
 
   // Returns the display mode of |display_id| which is currently used.
   DisplayMode GetActiveModeForDisplayId(int64 display_id) const;
 
   // Returns the display's selected mode. This returns false and doesn't
   // set |mode_out| if the display mode is in default.
   bool GetSelectedModeForDisplayId(int64 display_id,
                                    DisplayMode* mode_out) const;
 
@@ skipping 178 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_