Prepare ScreenWin To Use Per-Monitor DPI

ui/display/win/dpi.cc

 // 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.
 
 #include "ui/display/win/dpi.h"
 
 #include <windows.h>
 
 #include "base/win/scoped_hdc.h"
 #include "ui/display/display.h"
@@ skipping 20 matching lines @@
     // to all screens.
     dpi_x = GetDeviceCaps(screen_dc, LOGPIXELSX);
     dpi_y = GetDeviceCaps(screen_dc, LOGPIXELSY);
   }
   return gfx::Size(dpi_x, dpi_y);
 }
 
 float GetUnforcedDeviceScaleFactor() {
   return g_device_scale_factor
       ? g_device_scale_factor
-      : static_cast<float>(GetDPI().width()) / kDefaultDPI;
+      : GetScalingFactorFromDPI(GetDPI().width());
 }
 
 }  // namespace
 
 void SetDefaultDeviceScaleFactor(float scale) {
   DCHECK_NE(0.f, scale);
   g_device_scale_factor = scale;
 }
 
 float GetDPIScale() {
   if (display::Display::HasForceDeviceScaleFactor())
     return display::Display::GetForcedDeviceScaleFactor();
   float dpi_scale = GetUnforcedDeviceScaleFactor();
   return (dpi_scale <= 1.25f) ? 1.f : dpi_scale;
 }
 
 int GetDPIFromScalingFactor(float device_scaling_factor) {
   return kDefaultDPI * device_scaling_factor;
 }
 
+float GetScalingFactorFromDPI(int dpi) {
+  return static_cast<float>(dpi) / kDefaultDPI;
+}
+
 int GetSystemMetricsInDIP(int metric) {
   // The system metrics always reflect the system DPI, not whatever scale we've
   // forced or decided to use.
   return static_cast<int>(
       std::round(GetSystemMetrics(metric) / GetUnforcedDeviceScaleFactor()));
 }
 
 }  // namespace win
 }  // namespace display