Fix --force-device-scale-factor on Mac

ui/gfx/screen_mac.mm

 // 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.
 
 #include "ui/gfx/screen.h"
 
 #import <ApplicationServices/ApplicationServices.h>
 #import <Cocoa/Cocoa.h>
 
 #include <map>
@@ skipping 57 matching lines @@
     display.set_work_area(work_area);
   } else {
     display.set_bounds(ConvertCoordinateSystem(frame));
     display.set_work_area(ConvertCoordinateSystem(visible_frame));
   }
   CGFloat scale;
   if ([screen respondsToSelector:@selector(backingScaleFactor)])
     scale = [screen backingScaleFactor];
   else
     scale = [screen userSpaceScaleFactor];
+
+  if (gfx::Display::HasForceDeviceScaleFactor())
+    scale = gfx::Display::GetForcedDeviceScaleFactor();
+
   display.set_device_scale_factor(scale);
   // CGDisplayRotation returns a double. Display::SetRotationAsDegree will
   // handle the unexpected situations were the angle is not a multiple of 90.
   display.SetRotationAsDegree(static_cast<int>(CGDisplayRotation(display_id)));
   return display;
 }
 
 class ScreenMac : public gfx::Screen {
  public:
   ScreenMac() {
@@ skipping 181 matching lines @@
 
 namespace gfx {
 
 #if !defined(USE_AURA)
 Screen* CreateNativeScreen() {
   return new ScreenMac;
 }
 #endif
 
 }