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

ash/touch/touch_observer_hud.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/touch/touch_observer_hud.h"
 
 #include "ash/root_window_controller.h"
 #include "ash/root_window_settings.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
@@ skipping 28 matching lines @@
   params.parent =
       Shell::GetContainer(root_window_, kShellWindowId_OverlayContainer);
   widget_->Init(params);
   widget_->SetContentsView(content);
   widget_->StackAtTop();
   widget_->Show();
 
   widget_->AddObserver(this);
 
   // Observe changes in display size and mode to update touch HUD.
-  Shell::GetScreen()->AddObserver(this);
+  gfx::Screen::GetScreen()->AddObserver(this);
 #if defined(OS_CHROMEOS)
   Shell::GetInstance()->display_configurator()->AddObserver(this);
 #endif  // defined(OS_CHROMEOS)
 
   Shell::GetInstance()->window_tree_host_manager()->AddObserver(this);
   root_window_->AddPreTargetHandler(this);
 }
 
 TouchObserverHUD::~TouchObserverHUD() {
   Shell::GetInstance()->window_tree_host_manager()->RemoveObserver(this);
 
 #if defined(OS_CHROMEOS)
   Shell::GetInstance()->display_configurator()->RemoveObserver(this);
 #endif  // defined(OS_CHROMEOS)
-  Shell::GetScreen()->RemoveObserver(this);
+  gfx::Screen::GetScreen()->RemoveObserver(this);
 
   widget_->RemoveObserver(this);
 }
 
 void TouchObserverHUD::Clear() {
 }
 
 void TouchObserverHUD::Remove() {
   root_window_->RemovePreTargetHandler(this);
 
@@ skipping 69 matching lines @@
       widget_->GetNativeView(),
       Shell::GetContainer(root_window_, kShellWindowId_OverlayContainer));
 
   RootWindowController* controller = GetRootWindowController(root_window_);
   SetHudForRootWindowController(controller);
 
   root_window_->AddPreTargetHandler(this);
 }
 
 }  // namespace ash