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

components/sync/driver/sync_api_component_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 COMPONENTS_SYNC_DRIVER_SYNC_API_COMPONENT_FACTORY_H_
 #define COMPONENTS_SYNC_DRIVER_SYNC_API_COMPONENT_FACTORY_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 100 matching lines @@
       std::unique_ptr<DataTypeErrorHandler> error_handler) = 0;
 
   // Creates attachment service.
   // Note: Should only be called from the model type thread.
   //
   // |store_birthday| is the store birthday.  Must not be empty.
   //
   // |model_type| is the model type this AttachmentService will be used with.
   //
   // |delegate| is optional delegate for AttachmentService to notify about
-  // asynchronous events (AttachmentUploaded). Pass NULL if delegate is not
+  // asynchronous events (AttachmentUploaded). Pass null if delegate is not
   // provided. AttachmentService doesn't take ownership of delegate, the pointer
   // must be valid throughout AttachmentService lifetime.
   virtual std::unique_ptr<AttachmentService> CreateAttachmentService(
       std::unique_ptr<AttachmentStoreForSync> attachment_store,
       const UserShare& user_share,
       const std::string& store_birthday,
       ModelType model_type,
       AttachmentService::Delegate* delegate) = 0;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_DRIVER_SYNC_API_COMPONENT_FACTORY_H_