[cros,de-hack] Get rid of singleton for the WebUILoginScreen.

chrome/browser/chromeos/login/login_display.cc

 // Copyright (c) 2011 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/login/login_display.h"
 
 namespace chromeos {
 
 LoginDisplay::Delegate::~Delegate() {}
 
 LoginDisplay::LoginDisplay(Delegate* delegate,
                            const gfx::Rect& background_bounds)
     : delegate_(delegate),
       parent_window_(NULL),
       background_bounds_(background_bounds) {
 }
 
 LoginDisplay::~LoginDisplay() {}
 
-void LoginDisplay::Destroy() {
-  delete this;
-}
-
 }  // namespace chromeos