Update SupportsUserData uses with unique_ptr.

components/user_prefs/user_prefs.h

 // 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.
 
 #ifndef COMPONENTS_USER_PREFS_USER_PREFS_H_
 #define COMPONENTS_USER_PREFS_USER_PREFS_H_
 
 #include "base/macros.h"
 #include "base/supports_user_data.h"
 #include "components/user_prefs/user_prefs_export.h"
 
 class PrefService;
 
 namespace user_prefs {
 
 // Components may use preferences associated with a given user. These hang off
 // of base::SupportsUserData and can be retrieved using UserPrefs::Get().
 //
 // It is up to the embedder to create and own the PrefService and attach it to
 // base::SupportsUserData using the UserPrefs::Set() function.
 class USER_PREFS_EXPORT UserPrefs : public base::SupportsUserData::Data {
  public:
+  ~UserPrefs() override;
+
   // Retrieves the PrefService for a given context, or null if none is attached.
   static PrefService* Get(base::SupportsUserData* context);
 
   // Hangs the specified |prefs| off of |context|. Should be called
   // only once per context.
   static void Set(base::SupportsUserData* context, PrefService* prefs);
 
  private:
   explicit UserPrefs(PrefService* prefs);
-  ~UserPrefs() override;
 
   // Non-owning; owned by embedder.
   PrefService* prefs_;
 
   DISALLOW_COPY_AND_ASSIGN(UserPrefs);
 };
 
 }  // namespace user_prefs
 
 #endif  // COMPONENTS_USER_PREFS_USER_PREFS_H_