Make win_aura work without ash.

ui/aura/desktop/desktop_screen_win.h

+// 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.
+
+#ifndef UI_AURA_DESKTOP_DESKTOP_SCREEN_WIN_H_
+#define UI_AURA_DESKTOP_DESKTOP_SCREEN_WIN_H_
+#pragma once
+
+#include "ui/aura/aura_export.h"
+#include "ui/gfx/screen_impl.h"
+
+namespace aura {
+
+class AURA_EXPORT DesktopScreenWin : public gfx::ScreenImpl {
+public:
+  DesktopScreenWin();
+  virtual ~DesktopScreenWin();
+
+  // Overridden from gfx::ScreenImpl:
+  virtual gfx::Point GetCursorScreenPoint() OVERRIDE;
+  virtual gfx::NativeWindow GetWindowAtCursorScreenPoint() OVERRIDE;
+  virtual int GetNumMonitors() OVERRIDE;
+  virtual gfx::Monitor GetMonitorNearestWindow(
+      gfx::NativeView window) const OVERRIDE;
+  virtual gfx::Monitor GetMonitorNearestPoint(
+      const gfx::Point& point) const OVERRIDE;
+  virtual gfx::Monitor GetPrimaryMonitor() const OVERRIDE;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(DesktopScreenWin);
+};
+
+}  // namespace aura
+
+#endif  // UI_AURA_DESKTOP_DESKTOP_SCREEN_WIN_H_