Moves couple of WmShell methods to standalone functions

chrome/browser/chromeos/arc/boot_phase_monitor/arc_instance_throttle.cc

 // Copyright 2017 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/arc/boot_phase_monitor/arc_instance_throttle.h"
 
-#include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
 #include "ash/shared/app_types.h"
 #include "ash/shell.h"
+#include "ash/wm/window_util.h"
 #include "base/bind.h"
 #include "base/logging.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "chromeos/dbus/session_manager_client.h"
 #include "ui/wm/public/activation_client.h"
 
 namespace arc {
 
 namespace {
 
@@ skipping 25 matching lines @@
           ? login_manager::CONTAINER_CPU_RESTRICTION_BACKGROUND
           : login_manager::CONTAINER_CPU_RESTRICTION_FOREGROUND;
   session_manager_client->SetArcCpuRestriction(state,
                                                base::Bind(OnDBusReply, state));
 }
 
 }  // namespace
 
 ArcInstanceThrottle::ArcInstanceThrottle() {
   ash::Shell::GetInstance()->activation_client()->AddObserver(this);
-  ThrottleInstanceIfNeeded(ash::WmShell::Get()->GetActiveWindow());
+  ThrottleInstanceIfNeeded(ash::WmWindow::Get(ash::wm::GetActiveWindow()));
 }
 
 ArcInstanceThrottle::~ArcInstanceThrottle() {
   if (ash::Shell::HasInstance())
     ash::Shell::GetInstance()->activation_client()->RemoveObserver(this);
 }
 
 void ArcInstanceThrottle::OnWindowActivated(ActivationReason reason,
                                             aura::Window* gained_active,
                                             aura::Window* lost_active) {
   ThrottleInstanceIfNeeded(ash::WmWindow::Get(gained_active));
 }
 
 }  // namespace arc