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

ash/wm/maximize_mode/maximize_mode_window_manager.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/wm/maximize_mode/maximize_mode_window_manager.h"
 
 #include "ash/ash_switches.h"
 #include "ash/root_window_controller.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
@@ skipping 29 matching lines @@
 }  // namespace
 
 MaximizeModeWindowManager::~MaximizeModeWindowManager() {
   // Overview mode needs to be ended before exiting maximize mode to prevent
   // transforming windows which are currently in
   // overview: http://crbug.com/366605
   CancelOverview();
 
   Shell::GetInstance()->RemovePreTargetHandler(this);
   Shell::GetInstance()->RemoveShellObserver(this);
-  Shell::GetScreen()->RemoveObserver(this);
+  gfx::Screen::GetScreen()->RemoveObserver(this);
   EnableBackdropBehindTopWindowOnEachDisplay(false);
   RemoveWindowCreationObservers();
   RestoreAllWindows();
 }
 
 int MaximizeModeWindowManager::GetNumberOfManagedWindows() {
   return window_state_map_.size();
 }
 
 void MaximizeModeWindowManager::AddWindow(aura::Window* window) {
@@ skipping 127 matching lines @@
 
 MaximizeModeWindowManager::MaximizeModeWindowManager()
       : backdrops_hidden_(false) {
   // The overview mode needs to be ended before the maximize mode is started. To
   // guarantee the proper order, it will be turned off from here.
   CancelOverview();
 
   MaximizeAllWindows();
   AddWindowCreationObservers();
   EnableBackdropBehindTopWindowOnEachDisplay(true);
-  Shell::GetScreen()->AddObserver(this);
+  gfx::Screen::GetScreen()->AddObserver(this);
   Shell::GetInstance()->AddShellObserver(this);
   Shell::GetInstance()->AddPreTargetHandler(this);
 }
 
 void MaximizeModeWindowManager::MaximizeAllWindows() {
   MruWindowTracker::WindowList windows = ash::Shell::GetInstance()->
       mru_window_tracker()->BuildWindowListIgnoreModal();
   // Add all existing Mru windows.
   for (MruWindowTracker::WindowList::iterator window = windows.begin();
       window != windows.end(); ++window) {
@@ skipping 115 matching lines @@
     RootWindowController* controller = *iter;
     aura::Window* container = Shell::GetContainer(
         controller->GetRootWindow(), kShellWindowId_DefaultContainer);
     controller->workspace_controller()->SetMaximizeBackdropDelegate(
         scoped_ptr<WorkspaceLayoutManagerDelegate>(
             enable ? new WorkspaceBackdropDelegate(container) : NULL));
   }
 }
 
 }  // namespace ash