Use ScopedObserver to observe the SupervisedUserSyncService in SupervisedUserImportHandler.

chrome/browser/ui/webui/options/supervised_user_import_handler.h

 // Copyright 2014 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 CHROME_BROWSER_UI_WEBUI_OPTIONS_SUPERVISED_USER_IMPORT_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_OPTIONS_SUPERVISED_USER_IMPORT_HANDLER_H_
 
 #include <string>
 
 #include "base/callback_list.h"
 #include "base/memory/weak_ptr.h"
 #include "base/scoped_observer.h"
 #include "base/strings/string16.h"
 #include "chrome/browser/profiles/profile_info_cache_observer.h"
 #include "chrome/browser/supervised_user/legacy/supervised_user_sync_service_observer.h"
 #include "chrome/browser/ui/webui/options/options_ui.h"
 #include "components/signin/core/browser/signin_error_controller.h"
 
 namespace base {
 class DictionaryValue;
 class ListValue;
 }
 
 class ProfileInfoCache;
+class SupervisedUserSyncService;
 
 namespace options {
 
 // Handler for the 'import existing supervised user' dialog.
 class SupervisedUserImportHandler : public OptionsPageUIHandler,
                                     public ProfileInfoCacheObserver,
                                     public SupervisedUserSyncServiceObserver,
                                     public SigninErrorController::Observer {
  public:
   typedef base::CallbackList<void(const std::string&, const std::string&)>
@@ skipping 58 matching lines @@
   // changed, FetchSupervisedUsers() is called.
   void OnSharedSettingChanged(const std::string& supervised_user_id,
                               const std::string& key);
 
   scoped_ptr<CallbackList::Subscription> subscription_;
 
   ScopedObserver<ProfileInfoCache, SupervisedUserImportHandler>
       profile_observer_;
   ScopedObserver<SigninErrorController, SupervisedUserImportHandler>
       signin_error_observer_;
+  ScopedObserver<SupervisedUserSyncService, SupervisedUserImportHandler>
+      supervised_user_sync_service_observer_;
 
   bool removed_profile_is_supervised_;
 
   base::WeakPtrFactory<SupervisedUserImportHandler> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SupervisedUserImportHandler);
 };
 
 }  // namespace options
 
 #endif  // CHROME_BROWSER_UI_WEBUI_OPTIONS_SUPERVISED_USER_IMPORT_HANDLER_H_