Enable hidpi on Linux, refactor a bit on Windows to share

ui/base/layout.cc

Index: ui/base/layout.cc
diff --git a/ui/base/layout.cc b/ui/base/layout.cc
index aa3aecf55bd625d891f75339c8971406370f7e2f..cfbf10c5ab32a82330d857436d6c21937a99d84b 100644
--- a/ui/base/layout.cc
+++ b/ui/base/layout.cc
@@ -15,12 +15,12 @@
 #include "ui/base/touch/touch_device.h"
 #include "ui/base/ui_base_switches.h"
 #include "ui/gfx/display.h"
+#include "ui/gfx/dpi.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/gfx/screen.h"
 
 #if defined(OS_WIN)
 #include "base/win/metro.h"
-#include "ui/gfx/win/dpi.h"
 #include <Windows.h>
 #endif  // defined(OS_WIN)
 
@@ -85,7 +85,7 @@ ScaleFactor GetSupportedScaleFactor(float scale) {
 float GetImageScale(ScaleFactor scale_factor) {
 #if defined(OS_WIN)
   if (gfx::IsHighDPIEnabled())
-    return gfx::win::GetDeviceScaleFactor();
+    return gfx::GetDeviceScaleFactor();
 #endif
   return GetScaleForScaleFactor(scale_factor);
 }