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

ash/display/resolution_notification_controller.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/display/resolution_notification_controller.h"
 
 #include <utility>
 
 #include "ash/display/display_info.h"
 #include "ash/display/display_manager.h"
@@ skipping 134 matching lines @@
     timeout_count = kTimeoutInSec;
   }
 }
 
 ResolutionNotificationController::ResolutionChangeInfo::
     ~ResolutionChangeInfo() {
 }
 
 ResolutionNotificationController::ResolutionNotificationController() {
   Shell::GetInstance()->window_tree_host_manager()->AddObserver(this);
-  Shell::GetScreen()->AddObserver(this);
+  gfx::Screen::GetScreen()->AddObserver(this);
 }
 
 ResolutionNotificationController::~ResolutionNotificationController() {
   Shell::GetInstance()->window_tree_host_manager()->RemoveObserver(this);
-  Shell::GetScreen()->RemoveObserver(this);
+  gfx::Screen::GetScreen()->RemoveObserver(this);
 }
 
 void ResolutionNotificationController::PrepareNotification(
     int64_t display_id,
     const DisplayMode& old_resolution,
     const DisplayMode& new_resolution,
     const base::Closure& accept_callback) {
   DCHECK(!gfx::Display::IsInternalDisplayId(display_id));
   // If multiple resolution changes are invoked for the same display,
   // the original resolution for the first resolution change has to be used
@@ skipping 132 matching lines @@
                               this,
                               &ResolutionNotificationController::OnTimerTick);
   }
 }
 
 void ResolutionNotificationController::SuppressTimerForTest() {
   g_use_timer = false;
 }
 
 }  // namespace ash