Get the default device scale factor from monitor

ui/gfx/monitor.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 UI_GFX_MONITOR_H_
 #define UI_GFX_MONITOR_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "ui/base/ui_export.h"
 #include "ui/gfx/rect.h"
 
 namespace gfx {
 
 // Note: The screen and monitor currently uses pixel coordinate
 // system. With ENABLE_DIP macro (which is enabled with enable_dip=1
 // gyp flag), |bounds()| and |work_area| will return values in DIP
 // coordinate system, not in backing pixels.
 // TODO(oshima): Update the comment when ENABLE_DIP macro is removed.
 class UI_EXPORT Monitor {
  public:
+  // Returns the default value for the device scale factor, which is
+  // given by "--default-device-scale-factor".
+  static float GetDefaultDeviceScaleFactor();
+
   // Creates a monitor with invalid id(-1) as default.
   Monitor();
   explicit Monitor(int id);
   Monitor(int id, const Rect& bounds);
   ~Monitor();
 
   // Sets/Gets unique identifier associated with the monitor.
   int id() const { return id_; }
   void set_id(int id) { id_ = id; }
 
@@ skipping 49 matching lines @@
   Rect work_area_;
 #if defined(USE_ASH)
   Rect bounds_in_pixel_;
 #endif
   float device_scale_factor_;
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_MONITOR_H_