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

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.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_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_
 #define UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_
 
 #include <X11/extensions/shape.h>
 #include <X11/Xlib.h>
 
@@ skipping 325 matching lines @@
   // the frame when |xwindow_| gains focus or handles a mouse button event.
   bool urgency_hint_set_;
 
   base::CancelableCallback<void()> delayed_resize_task_;
 
   base::WeakPtrFactory<DesktopWindowTreeHostX11> close_widget_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopWindowTreeHostX11);
 };
 
+gfx::Point ScreenToDIPPoint(const gfx::Point& pixel_point);
+gfx::Point DIPToScreenPoint(const gfx::Point& dip_point);
+gfx::Size ScreenToDIPSize(const gfx::Size& size_in_pixels);
+gfx::Size DIPToScreenSize(const gfx::Size& dip_size);
+gfx::Rect DIPToScreenRect(const gfx::Rect& dip_bounds);
+gfx::Rect ScreenToDIPRect(const gfx::Rect& pixel_bounds);
+
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_