Clean-up of the system shutdown code paths

ash/test/test_system_tray_delegate.cc

 // 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.
 
 #include "ash/test/test_system_tray_delegate.h"
 
 #include <string>
 
 #include "ash/session/session_state_delegate.h"
 #include "ash/shell.h"
@@ skipping 76 matching lines @@
   return session_length_limit_set_;
 }
 
 bool TestSystemTrayDelegate::GetSessionLengthLimit(
     base::TimeDelta* session_length_limit) {
   if (session_length_limit_set_)
     *session_length_limit = session_length_limit_;
   return session_length_limit_set_;
 }
 
-void TestSystemTrayDelegate::ShutDown() {
-  base::MessageLoop::current()->Quit();
-}
-
 void TestSystemTrayDelegate::SignOut() {
   base::MessageLoop::current()->Quit();
 }
 
 }  // namespace test
 }  // namespace ash