Convert //ios from scoped_ptr to std::unique_ptr.

ios/chrome/browser/tab_parenting_global_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 "ios/chrome/browser/tab_parenting_global_observer.h"
 
 #include "base/memory/singleton.h"
 
 TabParentingGlobalObserver* TabParentingGlobalObserver::GetInstance() {
   return base::Singleton<TabParentingGlobalObserver>::get();
 }
 
-scoped_ptr<base::CallbackList<void(web::WebState*)>::Subscription>
+std::unique_ptr<base::CallbackList<void(web::WebState*)>::Subscription>
 TabParentingGlobalObserver::RegisterCallback(const OnTabParentedCallback& cb) {
   return on_tab_parented_callback_list_.Add(cb);
 }
 
 void TabParentingGlobalObserver::OnTabParented(web::WebState* web_state) {
   on_tab_parented_callback_list_.Notify(web_state);
 }
 
 TabParentingGlobalObserver::TabParentingGlobalObserver() {}
 
 TabParentingGlobalObserver::~TabParentingGlobalObserver() {}