Prepare ScreenWin To Use Per-Monitor DPI

ui/display/win/dpi.h

 // Copyright 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_DISPLAY_WIN_DPI_H_
 #define UI_DISPLAY_WIN_DPI_H_
 
 #include "ui/display/display_export.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace display {
 namespace win {
 
 // Sets the device scale factor that will be used unless overridden on the
 // command line by --force-device-scale-factor.  If this is not called, and that
 // flag is not used, the scale factor used by the DIP conversion functions below
 // will be that returned by GetDPIScale().
 DISPLAY_EXPORT void SetDefaultDeviceScaleFactor(float scale);
 
 // Gets the scale factor of the display. For example, if the display DPI is
 // 96 then the scale factor is 1.0.  This clamps scale factors <= 1.25 to 1.0 to
 // maintain previous (non-DPI-aware) behavior where only the font size was
 // boosted.
 DISPLAY_EXPORT float GetDPIScale();
 
 // Returns the equivalent DPI for |device_scaling_factor|.
 DISPLAY_EXPORT int GetDPIFromScalingFactor(float device_scaling_factor);
 
+// Returns the equivalent scaling factor for |dpi|.
+DISPLAY_EXPORT float GetScalingFactorFromDPI(int dpi);
+
 // Win32's GetSystemMetrics uses pixel measures. This function calls
 // GetSystemMetrics for the given |metric|, then converts the result to DIP.
 DISPLAY_EXPORT int GetSystemMetricsInDIP(int metric);
 
 }  // namespace win
 }  // namespace display
 
 #endif  // UI_DISPLAY_WIN_DPI_H_