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

components/sync/driver/glue/sync_backend_registrar.h

 // Copyright 2012 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_REGISTRAR_H_
 #define COMPONENTS_SYNC_DRIVER_GLUE_SYNC_BACKEND_REGISTRAR_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 133 matching lines @@
 
   // Add a worker for |group| to the worker map if one can be created.
   void MaybeAddWorker(ModelSafeGroup group);
 
   // Callback after workers unregister from observing destruction of their
   // working loops.
   void OnWorkerUnregistrationDone(ModelSafeGroup group);
 
   void RemoveWorker(ModelSafeGroup group);
 
-  // Returns the change processor for the given model, or NULL if none
+  // Returns the change processor for the given model, or null if none
   // exists.  Must be called from |group|'s native thread.
   ChangeProcessor* GetProcessor(ModelType type) const;
 
   // Must be called with |lock_| held.  Simply returns the change
   // processor for the given type, if it exists.  May be called from
   // any thread.
   ChangeProcessor* GetProcessorUnsafe(ModelType type) const;
 
   // Return true if |model_type| lives on the current thread.  Must be
   // called with |lock_| held.  May be called on any thread.
@@ skipping 54 matching lines @@
   // Set of types with non-blocking implementation (as opposed to directory
   // based).
   ModelTypeSet non_blocking_types_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncBackendRegistrar);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_DRIVER_GLUE_SYNC_BACKEND_REGISTRAR_H_