[Sync] Replacing NULL with nullptr/null throughout sync code.

chrome/browser/sync/sync_global_error_factory.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_SYNC_SYNC_GLOBAL_ERROR_FACTORY_H_
 #define CHROME_BROWSER_SYNC_SYNC_GLOBAL_ERROR_FACTORY_H_
 
 #include "base/macros.h"
 #include "base/memory/singleton.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
 class SyncGlobalError;
 class Profile;
 
 // Singleton that owns all SyncGlobalErrors and associates them with
 // Profiles. Listens for the Profile's destruction notification and cleans up
 // the associated SyncGlobalError.
 class SyncGlobalErrorFactory : public BrowserContextKeyedServiceFactory {
  public:
   // Returns the instance of SyncGlobalError associated with this profile,
-  // creating one if none exists. In Ash, this will return NULL.
+  // creating one if none exists. In Ash, this will return null.
   static SyncGlobalError* GetForProfile(Profile* profile);
 
   // Returns an instance of the SyncGlobalErrorFactory singleton.
   static SyncGlobalErrorFactory* GetInstance();
 
  private:
   friend struct base::DefaultSingletonTraits<SyncGlobalErrorFactory>;
 
   SyncGlobalErrorFactory();
   ~SyncGlobalErrorFactory() override;
 
   // BrowserContextKeyedServiceFactory:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* profile) const override;
 
   DISALLOW_COPY_AND_ASSIGN(SyncGlobalErrorFactory);
 };
 
 #endif  // CHROME_BROWSER_SYNC_SYNC_GLOBAL_ERROR_FACTORY_H_