Refactor ViewsDelegate singleton

ui/views/win/windows_session_change_observer.cc

 // Copyright 2015 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 "ui/views/win/windows_session_change_observer.h"
 
 #include <wtsapi32.h>
 #pragma comment(lib, "wtsapi32.lib")
 
 #include "base/bind.h"
@@ skipping 49 matching lines @@
         break;
     }
   }
 
   void AddSingletonHwndObserver() {
     DCHECK(!singleton_hwnd_observer_);
     singleton_hwnd_observer_.reset(new gfx::SingletonHwndObserver(
         base::Bind(&WtsRegistrationNotificationManager::OnWndProc,
                    base::Unretained(this))));
     scoped_refptr<base::TaskRunner> task_runner;
-    if (ViewsDelegate::views_delegate) {
-      task_runner = ViewsDelegate::views_delegate->GetBlockingPoolTaskRunner();
+    if (ViewsDelegate::GetInstance()) {
+      task_runner = ViewsDelegate::GetInstance()->GetBlockingPoolTaskRunner();
     }
 
     base::Closure wts_register =
         base::Bind(base::IgnoreResult(&WTSRegisterSessionNotification),
                    gfx::SingletonHwnd::GetInstance()->hwnd(),
                    NOTIFY_FOR_THIS_SESSION);
     if (task_runner) {
       task_runner->PostTask(FROM_HERE, wts_register);
     } else {
       wts_register.Run();
@@ skipping 39 matching lines @@
 }
 
 void WindowsSessionChangeObserver::ClearCallback() {
   if (!callback_.is_null()) {
     callback_.Reset();
     WtsRegistrationNotificationManager::GetInstance()->RemoveObserver(this);
   }
 }
 
 }  // namespace views