mash: Migrate remaining tray observers and notify functions.

ash/system/chromeos/session/last_window_closed_logout_reminder.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/system/chromeos/session/last_window_closed_logout_reminder.h"
 
 #include "ash/common/login_status.h"
 #include "ash/common/system/tray/system_tray_delegate.h"
+#include "ash/common/system/tray/system_tray_notifier.h"
 #include "ash/common/wm_shell.h"
 #include "ash/shell.h"
 #include "ash/system/chromeos/session/logout_confirmation_controller.h"
-#include "ash/system/tray/system_tray_notifier.h"
 #include "base/time/time.h"
 
 namespace ash {
 namespace {
 const int kLogoutConfirmationDelayInSeconds = 20;
 }
 
 LastWindowClosedLogoutReminder::LastWindowClosedLogoutReminder() {
-  Shell::GetInstance()->system_tray_notifier()->AddLastWindowClosedObserver(
-      this);
+  WmShell::Get()->system_tray_notifier()->AddLastWindowClosedObserver(this);
 }
 
 LastWindowClosedLogoutReminder::~LastWindowClosedLogoutReminder() {
-  Shell::GetInstance()->system_tray_notifier()->RemoveLastWindowClosedObserver(
-      this);
+  WmShell::Get()->system_tray_notifier()->RemoveLastWindowClosedObserver(this);
 }
 
 void LastWindowClosedLogoutReminder::OnLastWindowClosed() {
   if (WmShell::Get()->system_tray_delegate()->GetUserLoginStatus() !=
       LoginStatus::PUBLIC) {
     return;
   }
 
   // Ask the user to confirm logout if a public session is in progress and the
   // screen is not locked.
   Shell::GetInstance()->logout_confirmation_controller()->ConfirmLogout(
       base::TimeTicks::Now() +
       base::TimeDelta::FromSeconds(kLogoutConfirmationDelayInSeconds));
 }
 
 }  // namespace ash