[SyncFS] Use nullptr for scoped_ptr initialization

chrome/browser/sync_file_system/drive_backend/sync_worker_unittest.cc

 // 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.
 
 #include "chrome/browser/sync_file_system/drive_backend/sync_worker.h"
 
 #include "base/files/scoped_temp_dir.h"
 #include "base/run_loop.h"
 #include "base/strings/stringprintf.h"
 #include "base/thread_task_runner_handle.h"
@@ skipping 97 matching lines @@
     ASSERT_TRUE(profile_dir_.CreateUniqueTempDir());
     in_memory_env_.reset(leveldb::NewMemEnv(leveldb::Env::Default()));
 
     extension_service_.reset(new MockExtensionService);
     scoped_ptr<drive::DriveServiceInterface>
         fake_drive_service(new drive::FakeDriveService);
 
     scoped_ptr<SyncEngineContext>
         sync_engine_context(new SyncEngineContext(
             fake_drive_service.Pass(),
-            scoped_ptr<drive::DriveUploaderInterface>(),
+            nullptr /* drive_uploader */,
             nullptr /* task_logger */,
             base::ThreadTaskRunnerHandle::Get() /* ui_task_runner */,
             base::ThreadTaskRunnerHandle::Get() /* worker_task_runner */));
 
     sync_worker_.reset(new SyncWorker(
         profile_dir_.path(),
         extension_service_->AsWeakPtr(),
         in_memory_env_.get()));
     sync_worker_->Initialize(sync_engine_context.Pass());
 
@@ skipping 252 matching lines @@
       base::Bind(&SyncWorkerTest::CheckServiceState,
                  AsWeakPtr(),
                  SYNC_STATUS_OK,
                  REMOTE_SERVICE_OK));
 
   base::RunLoop().RunUntilIdle();
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system