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

ash/system/web_notification/ash_popup_alignment_delegate.cc

 // Copyright 2014 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/system/web_notification/ash_popup_alignment_delegate.h"
 
 #include "ash/display/window_tree_host_manager.h"
 #include "ash/screen_util.h"
 #include "ash/shelf/shelf_constants.h"
 #include "ash/shelf/shelf_layout_manager.h"
@@ skipping 112 matching lines @@
 void AshPopupAlignmentDelegate::UpdateShelf() {
   if (shelf_)
     return;
 
   shelf_ = ShelfLayoutManager::ForShelf(root_window_);
   if (shelf_)
     shelf_->AddObserver(this);
 }
 
 gfx::Display AshPopupAlignmentDelegate::GetCurrentDisplay() const {
-  return Shell::GetScreen()->GetDisplayNearestWindow(
+  return gfx::Screen::GetScreen()->GetDisplayNearestWindow(
       shelf_->shelf_widget()->GetNativeView());
 }
 
 void AshPopupAlignmentDelegate::UpdateWorkArea() {
   work_area_ = shelf_->user_work_area_bounds();
   DoUpdateIfPossible();
 }
 
 void AshPopupAlignmentDelegate::OnDisplayWorkAreaInsetsChanged() {
   UpdateShelf();
@@ skipping 20 matching lines @@
 
 void AshPopupAlignmentDelegate::OnDisplayMetricsChanged(
     const gfx::Display& display,
     uint32_t metrics) {
   UpdateShelf();
   if (shelf_ && GetCurrentDisplay().id() == display.id())
     UpdateWorkArea();
 }
 
 }  // namespace ash