[SyncFS] Use nullptr instead of NULL

chrome/browser/sync_file_system/drive_backend/register_app_task.cc

 // 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.
 
 #include "chrome/browser/sync_file_system/drive_backend/register_app_task.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "chrome/browser/drive/drive_api_util.h"
 #include "chrome/browser/drive/drive_service_interface.h"
@@ skipping 26 matching lines @@
       create_folder_retry_count_(0),
       app_id_(app_id),
       weak_ptr_factory_(this) {
 }
 
 RegisterAppTask::~RegisterAppTask() {
 }
 
 bool RegisterAppTask::CanFinishImmediately() {
   return metadata_database() &&
-         metadata_database()->FindAppRootTracker(app_id_, NULL);
+         metadata_database()->FindAppRootTracker(app_id_, nullptr);
 }
 
 void RegisterAppTask::RunExclusive(const SyncStatusCallback& callback) {
   if (create_folder_retry_count_++ >= kMaxRetry) {
     callback.Run(SYNC_STATUS_FAILED);
     return;
   }
 
   if (!metadata_database() || !drive_service()) {
     callback.Run(SYNC_STATUS_FAILED);
@@ skipping 118 matching lines @@
 MetadataDatabase* RegisterAppTask::metadata_database() {
   return sync_context_->GetMetadataDatabase();
 }
 
 drive::DriveServiceInterface* RegisterAppTask::drive_service() {
   return sync_context_->GetDriveService();
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system