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

ui/base/win/dpi_setup.h

Index: ui/base/win/dpi_setup.h
diff --git a/ui/base/win/dpi_setup.h b/ui/base/win/dpi_setup.h
deleted file mode 100644
index 5837153d9fd0beb57b32950dcfcdfb83fb387259..0000000000000000000000000000000000000000
--- a/ui/base/win/dpi_setup.h
+++ /dev/null
@@ -1,22 +0,0 @@
-// Copyright (c) 2013 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_BASE_WIN_DPI_SETUP_H_
-#define UI_BASE_WIN_DPI_SETUP_H_
-
-#include "ui/base/ui_base_export.h"
-
-namespace ui {
-namespace win {
-
-// Initializes the device scale factor. If support is enabled, this will set
-// the best available scale based on the screen's pixel density. This can be
-// affected (overridden) by --force-device-scale-factor=x
-// This function can be called only once for the lifetime of a process.
-UI_BASE_EXPORT void InitDeviceScaleFactor();
-
-}  // namespace win
-}  // namespace ui
-
-#endif  // UI_BASE_WIN_DPI_SETUP_H_