Clean-up of the system shutdown code paths

ash/test/test_system_tray_delegate.h

 // 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.
 
 #ifndef ASH_TEST_TEST_SYSTEM_TRAY_DELEGATE_H_
 #define ASH_TEST_TEST_SYSTEM_TRAY_DELEGATE_H_
 
 #include "ash/system/tray/default_system_tray_delegate.h"
 #include "base/time/time.h"
 
@@ skipping 29 matching lines @@
 
   // Clears the session length limit.
   void ClearSessionLengthLimit();
 
   // Overridden from SystemTrayDelegate:
   user::LoginStatus GetUserLoginStatus() const override;
   bool IsUserSupervised() const override;
   bool ShouldShowDisplayNotification() override;
   bool GetSessionStartTime(base::TimeTicks* session_start_time) override;
   bool GetSessionLengthLimit(base::TimeDelta* session_length_limit) override;
-  void ShutDown() override;
   void SignOut() override;
 
  private:
   bool should_show_display_notification_;
   user::LoginStatus login_status_;
   base::TimeDelta session_length_limit_;
   bool session_length_limit_set_;
 
   DISALLOW_COPY_AND_ASSIGN(TestSystemTrayDelegate);
 };
 
 }  // namespace test
 }  // namespace ash
 
 #endif  // ASH_TEST_TEST_SYSTEM_TRAY_DELEGATE_H_