Switch SupportsUserData uses to use unique_ptr.

components/history/ios/browser/web_state_top_sites_observer.h

 // 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.
 
 #ifndef COMPONENTS_HISTORY_IOS_BROWSER_WEB_STATE_TOP_SITES_OBSERVER_H_
 #define COMPONENTS_HISTORY_IOS_BROWSER_WEB_STATE_TOP_SITES_OBSERVER_H_
 
 #include "base/macros.h"
 #include "ios/web/public/web_state/web_state_observer.h"
 #include "ios/web/public/web_state/web_state_user_data.h"
 
 namespace history {
 
 class TopSites;
 
 // WebStateTopSitesObserver forwards navigation events from web::WebState to
 // TopSites.
 class WebStateTopSitesObserver
     : public web::WebStateObserver,
       public web::WebStateUserData<WebStateTopSitesObserver> {
  public:
+  ~WebStateTopSitesObserver() override;
+
   static void CreateForWebState(web::WebState* web_state, TopSites* top_sites);
 
  private:
   friend class web::WebStateUserData<WebStateTopSitesObserver>;
 
   WebStateTopSitesObserver(web::WebState* web_state, TopSites* top_sites);
-  ~WebStateTopSitesObserver() override;
 
   // web::WebStateObserver implementation.
   void NavigationItemCommitted(
       const web::LoadCommittedDetails& load_details) override;
 
   // Underlying TopSites instance, may be null during testing.
   TopSites* top_sites_;
 
   DISALLOW_COPY_AND_ASSIGN(WebStateTopSitesObserver);
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_IOS_BROWSER_WEB_STATE_TOP_SITES_OBSERVER_H_