[SyncFS] Use nullptr instead of NULL

chrome/browser/sync_file_system/drive_backend/sync_engine_initializer.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/sync_engine_initializer.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/logging.h"
 #include "chrome/browser/drive/drive_api_service.h"
@@ skipping 180 matching lines @@
       continue;
 
     // Pick an orphaned folder or a direct child of the root folder and
     // ignore others.
     DCHECK(!root_folder_id_.empty());
     if (!HasNoParents(*entry) && !HasFolderAsParent(*entry, root_folder_id_))
       continue;
 
     if (!sync_root_folder_ || LessOnCreationTime(*entry, *sync_root_folder_)) {
       sync_root_folder_.reset(entry);
-      *itr = NULL;
+      *itr = nullptr;
     }
   }
 
   set_used_network(true);
   // If there are more results, retrieve them.
   if (!file_list->next_link().is_empty()) {
     cancel_callback_ = sync_context_->GetDriveService()->GetRemainingFileList(
         file_list->next_link(),
         base::Bind(&SyncEngineInitializer::DidFindSyncRoot,
                    weak_ptr_factory_.GetWeakPtr(),
@@ skipping 137 matching lines @@
     return;
   }
 
   util::Log(logging::LOG_VERBOSE, FROM_HERE,
             "[Initialize] Completed successfully.");
   SyncTaskManager::NotifyTaskDone(token.Pass(), SYNC_STATUS_OK);
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system