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

ash/wm/overview/window_selector.cc

 // Copyright 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.
 
 #include "ash/wm/overview/window_selector.h"
 
 #include <algorithm>
 #include <functional>
 #include <set>
 #include <utility>
@@ skipping 303 matching lines @@
         CreateTextFilter(this, Shell::GetPrimaryRootWindow()));
   }
 
   DCHECK(!grid_list_.empty());
   UMA_HISTOGRAM_COUNTS_100("Ash.WindowSelector.Items", num_items_);
 
   Shell* shell = Shell::GetInstance();
 
   shell->activation_client()->AddObserver(this);
 
-  shell->GetScreen()->AddObserver(this);
+  gfx::Screen::GetScreen()->AddObserver(this);
   shell->metrics()->RecordUserMetricsAction(UMA_WINDOW_OVERVIEW);
   // Send an a11y alert.
   shell->accessibility_delegate()->TriggerAccessibilityAlert(
       ui::A11Y_ALERT_WINDOW_OVERVIEW_MODE_ENTERED);
 
   UpdateShelfVisibility();
 }
 
 // NOTE: The work done in Shutdown() is not done in the destructor because it
 // may cause other, unrelated classes, (ie PanelLayoutManager) to make indirect
@@ skipping 43 matching lines @@
   grid_list_.clear();
   UpdateShelfVisibility();
 }
 
 void WindowSelector::RemoveAllObservers() {
   Shell* shell = Shell::GetInstance();
   for (aura::Window* window : observed_windows_)
     window->RemoveObserver(this);
 
   shell->activation_client()->RemoveObserver(this);
-  shell->GetScreen()->RemoveObserver(this);
+  gfx::Screen::GetScreen()->RemoveObserver(this);
   if (restore_focus_window_)
     restore_focus_window_->RemoveObserver(this);
 }
 
 void WindowSelector::CancelSelection() {
   delegate_->OnSelectionEnded();
 }
 
 void WindowSelector::OnGridEmpty(WindowGrid* grid) {
   ScopedVector<WindowGrid>::iterator iter =
@@ skipping 239 matching lines @@
   for (size_t i = 0;
       i <= grid_list_.size() &&
       grid_list_[selected_grid_index_]->Move(direction, animate); i++) {
     selected_grid_index_ =
         (selected_grid_index_ + display_direction + grid_list_.size()) %
         grid_list_.size();
   }
 }
 
 }  // namespace ash