Add context to gfx::Screen calls in support of simultaneous desktop+ash

chrome/browser/chromeos/display/primary_display_switch_observer.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 "chrome/browser/chromeos/display/primary_display_switch_observer.h"
 
 #include "ash/shell.h"
 #include "chrome/browser/chromeos/display/display_preferences.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "ui/aura/root_window.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/screen.h"
 
 namespace chromeos {
 
 void PrimaryDisplaySwitchObserver::OnRootWindowMoved(
     const aura::RootWindow* root_window, const gfx::Point& new_origin) {
-  StorePrimaryDisplayIDPref(gfx::Screen::GetPrimaryDisplay().id());
+  StorePrimaryDisplayIDPref(ash::Shell::GetScreen()->GetPrimaryDisplay().id());
 }
 
 PrimaryDisplaySwitchObserver::PrimaryDisplaySwitchObserver()
     : primary_root_(ash::Shell::GetInstance()->GetPrimaryRootWindow()) {
   primary_root_->AddRootWindowObserver(this);
 }
 
 PrimaryDisplaySwitchObserver::~PrimaryDisplaySwitchObserver() {
   primary_root_->RemoveRootWindowObserver(this);
 }
 
 }  // namespace chromeos