Remove now-unnecessary wrappers around gfx::Screen::GetScreen()

ash/wm/coordinate_conversion.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 "ash/wm/coordinate_conversion.h"
 
 #include "ash/display/window_tree_host_manager.h"
 #include "ash/shell.h"
 #include "ui/aura/client/screen_position_client.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/screen.h"
 
 namespace ash {
 namespace wm {
 
 aura::Window* GetRootWindowAt(const gfx::Point& point) {
   const gfx::Display& display =
-      Shell::GetScreen()->GetDisplayNearestPoint(point);
+      gfx::Screen::GetScreen()->GetDisplayNearestPoint(point);
   DCHECK(display.is_valid());
   // TODO(yusukes): Move coordinate_conversion.cc and .h to ui/aura/ once
   // GetRootWindowForDisplayId() is moved to aura::Env.
   return Shell::GetInstance()
       ->window_tree_host_manager()
       ->GetRootWindowForDisplayId(display.id());
 }
 
 aura::Window* GetRootWindowMatching(const gfx::Rect& rect) {
-  const gfx::Display& display = Shell::GetScreen()->GetDisplayMatching(rect);
+  const gfx::Display& display =
+      gfx::Screen::GetScreen()->GetDisplayMatching(rect);
   return Shell::GetInstance()
       ->window_tree_host_manager()
       ->GetRootWindowForDisplayId(display.id());
 }
 
 }  // namespace wm
 }  // namespace ash