[SyncFS] Use nullptr for scoped_ptr initialization

chrome/browser/sync_file_system/drive_backend/sync_engine.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.h"
 
 #include <vector>
 
 #include "base/bind.h"
 #include "base/metrics/histogram.h"
@@ skipping 266 matching lines @@
   if (!signin_manager_ || !signin_manager_->IsAuthenticated())
     return;
 
   DCHECK(drive_service_factory_);
   scoped_ptr<drive::DriveServiceInterface> drive_service =
       drive_service_factory_->CreateDriveService(
           token_service_, request_context_.get(), drive_task_runner_.get());
   scoped_ptr<drive::DriveUploaderInterface> drive_uploader(
       new drive::DriveUploader(drive_service.get(), drive_task_runner_.get()));
 
-  InitializeInternal(drive_service.Pass(), drive_uploader.Pass(),
-                     scoped_ptr<SyncWorkerInterface>());
+  InitializeInternal(drive_service.Pass(), drive_uploader.Pass(), nullptr);
 }
 
 void SyncEngine::InitializeForTesting(
     scoped_ptr<drive::DriveServiceInterface> drive_service,
     scoped_ptr<drive::DriveUploaderInterface> drive_uploader,
     scoped_ptr<SyncWorkerInterface> sync_worker) {
   Reset();
   InitializeInternal(drive_service.Pass(), drive_uploader.Pass(),
                      sync_worker.Pass());
 }
@@ skipping 502 matching lines @@
 
 SyncStatusCallback SyncEngine::TrackCallback(
     const SyncStatusCallback& callback) {
   return callback_tracker_.Register(
       base::Bind(callback, SYNC_STATUS_ABORT),
       callback);
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system