mash: Introduce WmSystemTrayNotifier for //ash/common

ash/system/tray_update_unittest.cc

 // Copyright 2016 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/tray_update.h"
 
-#include "ash/common/system/tray/system_tray_delegate.h"
+#include "ash/common/system/tray/wm_system_tray_notifier.h"
+#include "ash/common/wm_shell.h"
 #include "ash/shell.h"
 #include "ash/system/tray/system_tray.h"
-#include "ash/system/tray/system_tray_notifier.h"
 #include "ash/test/ash_test_base.h"
 #include "ash/test/test_system_tray_delegate.h"
 #include "base/macros.h"
 
 namespace ash {
 
 using TrayUpdateTest = test::AshTestBase;
 
 // Tests that the update icon becomes visible when an update becomes
 // available.
 TEST_F(TrayUpdateTest, VisibilityAfterUpdate) {
   TrayUpdate* tray_update =
       Shell::GetInstance()->GetPrimarySystemTray()->GetTrayUpdateForTesting();
 
   // The system starts with no update pending.
   test::TestSystemTrayDelegate* tray_delegate = GetSystemTrayDelegate();
   UpdateInfo initial_info;
   tray_delegate->GetSystemUpdateInfo(&initial_info);
   EXPECT_FALSE(initial_info.update_required);
 
   // When no update is pending, the item isn't visible.
   EXPECT_FALSE(tray_update->tray_view()->visible());
 
   // Simulate an update.
   UpdateInfo info;
   info.update_required = true;
-  Shell::GetInstance()->system_tray_notifier()->NotifyUpdateRecommended(info);
+  WmShell::Get()->system_tray_notifier()->NotifyUpdateRecommended(info);
 
   // Tray item is now visible.
   EXPECT_TRUE(tray_update->tray_view()->visible());
 }
 
 }  // namespace ash