Reland of Supervised Users: Create ResourceThrottle only if filtering is enabled

chrome/browser/supervised_user/supervised_user_service.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_SUPERVISED_USER_SUPERVISED_USER_SERVICE_H_
 #define CHROME_BROWSER_SUPERVISED_USER_SUPERVISED_USER_SERVICE_H_
 
 #include <stddef.h>
 
 #include <map>
@@ skipping 232 matching lines @@
   // lives on the IO thread. This class mediates access to them and makes sure
   // they are kept in sync.
   class URLFilterContext {
    public:
     URLFilterContext();
     ~URLFilterContext();
 
     SupervisedUserURLFilter* ui_url_filter() const;
     SupervisedUserURLFilter* io_url_filter() const;
 
+    void SetEnabled(bool enabled);
     void SetDefaultFilteringBehavior(
         SupervisedUserURLFilter::FilteringBehavior behavior);
     void LoadWhitelists(
         const std::vector<scoped_refptr<SupervisedUserSiteList>>& site_lists);
     // TODO(treib): Make SupervisedUserBlacklist refcounted, so the IO thread
     // will retain a reference to the blacklist.
     void SetBlacklist(const SupervisedUserBlacklist* blacklist);
     bool HasBlacklist() const;
     void SetManualHosts(std::unique_ptr<std::map<std::string, bool>> host_map);
     void SetManualURLs(std::unique_ptr<std::map<GURL, bool>> url_map);
@@ skipping 208 matching lines @@
 
   base::ObserverList<SupervisedUserServiceObserver> observer_list_;
 
   // Prevents Sync from running until configuration is complete.
   std::unique_ptr<syncer::SyncSetupInProgressHandle> sync_blocker_;
 
   base::WeakPtrFactory<SupervisedUserService> weak_ptr_factory_;
 };
 
 #endif  // CHROME_BROWSER_SUPERVISED_USER_SUPERVISED_USER_SERVICE_H_