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

ui/base/layout.cc

 // 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/base/layout.h"
 
 #include <algorithm>
 #include <cmath>
 #include <limits>
 
 #include "base/basictypes.h"
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "build/build_config.h"
 #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)
 
 namespace ui {
 
 namespace {
 
 bool ScaleFactorComparator(const ScaleFactor& lhs, const ScaleFactor& rhs){
   return GetScaleForScaleFactor(lhs) < GetScaleForScaleFactor(rhs);
 }
@@ skipping 44 matching lines @@
       smallest_diff = diff;
     }
   }
   DCHECK_NE(closest_match, SCALE_FACTOR_NONE);
   return closest_match;
 }
 
 float GetImageScale(ScaleFactor scale_factor) {
 #if defined(OS_WIN)
   if (gfx::IsHighDPIEnabled())
-    return gfx::win::GetDeviceScaleFactor();
+    return gfx::GetDeviceScaleFactor();
 #endif
   return GetScaleForScaleFactor(scale_factor);
 }
 
 float GetScaleForScaleFactor(ScaleFactor scale_factor) {
   return kScaleFactorScales[scale_factor];
 }
 
 namespace test {
 
@@ skipping 25 matching lines @@
   gfx::Screen* screen = gfx::Screen::GetScreenFor(view);
   if (screen->IsDIPEnabled()) {
     gfx::Display display = screen->GetDisplayNearestWindow(view);
     return display.device_scale_factor();
   }
   return 1.0f;
 }
 #endif  // !defined(OS_MACOSX)
 
 }  // namespace ui