[Sync] Replacing NULL with nullptr in code and null in comments for components/sync/

components/sync/driver/glue/sync_backend_host_core.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_SYNC_DRIVER_GLUE_SYNC_BACKEND_HOST_CORE_H_
 #define COMPONENTS_SYNC_DRIVER_GLUE_SYNC_BACKEND_HOST_CORE_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 250 matching lines @@
   // Name used for debugging.
   const std::string name_;
 
   // Path of the folder that stores the sync data files.
   const base::FilePath sync_data_folder_path_;
 
   // Our parent SyncBackendHost.
   WeakHandle<SyncBackendHostImpl> host_;
 
   // The loop where all the sync backend operations happen.
-  // Non-NULL only between calls to DoInitialize() and ~Core().
+  // Non-null only between calls to DoInitialize() and ~Core().
   base::MessageLoop* sync_loop_;
 
-  // Our parent's registrar (not owned).  Non-NULL only between
+  // Our parent's registrar (not owned).  Non-null only between
   // calls to DoInitialize() and DoShutdown().
   SyncBackendRegistrar* registrar_;
 
   // The timer used to periodically call SaveChanges.
   std::unique_ptr<base::RepeatingTimer> save_changes_timer_;
 
   // Our encryptor, which uses Chrome's encryption functions.
   SystemEncryptor encryptor_;
 
   // The top-level syncapi entry point.  Lives on the sync thread.
@@ skipping 30 matching lines @@
   std::map<ModelType, int64_t> last_invalidation_versions_;
 
   base::WeakPtrFactory<SyncBackendHostCore> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncBackendHostCore);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_DRIVER_GLUE_SYNC_BACKEND_HOST_CORE_H_