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

ash/shell/content/client/shell_browser_main_parts.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/shell/content/client/shell_browser_main_parts.h"
 
 #include "ash/ash_switches.h"
 #include "ash/content/shell_content_state.h"
 #include "ash/desktop_background/desktop_background_controller.h"
 #include "ash/shell.h"
@@ skipping 116 matching lines @@
 
   ash::ShellInitParams init_params;
   init_params.delegate = delegate_;
   init_params.context_factory = content::GetContextFactory();
   init_params.blocking_pool = content::BrowserThread::GetBlockingPool();
   ash::Shell::CreateInstance(init_params);
   ash::Shell::GetInstance()->CreateShelf();
   ash::Shell::GetInstance()->UpdateAfterLoginStatusChange(user::LOGGED_IN_USER);
 
   window_watcher_.reset(new ash::shell::WindowWatcher);
-  gfx::Screen* screen = Shell::GetInstance()->GetScreen();
-  screen->AddObserver(window_watcher_.get());
+  gfx::Screen::GetScreen()->AddObserver(window_watcher_.get());
 
   ash::shell::InitWindowTypeLauncher();
 
   ash::Shell::GetPrimaryRootWindow()->GetHost()->Show();
 }
 
 void ShellBrowserMainParts::PostMainMessageLoopRun() {
-  gfx::Screen* screen = Shell::GetInstance()->GetScreen();
-  screen->RemoveObserver(window_watcher_.get());
+  gfx::Screen::GetScreen()->RemoveObserver(window_watcher_.get());
 
   window_watcher_.reset();
   delegate_ = nullptr;
   ash::Shell::DeleteInstance();
   ShellContentState::DestroyInstance();
   // The global message center state must be shutdown absent
   // g_browser_process.
   message_center::MessageCenter::Shutdown();
 
 #if defined(OS_CHROMEOS)
@@ skipping 11 matching lines @@
   browser_context_.reset();
 }
 
 bool ShellBrowserMainParts::MainMessageLoopRun(int* result_code) {
   base::MessageLoopForUI::current()->Run();
   return true;
 }
 
 }  // namespace shell
 }  // namespace ash