[SyncFS] Use nullptr for scoped_ptr initialization

chrome/browser/sync_file_system/drive_backend/sync_task_token.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_task_token.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "base/thread_task_runner_handle.h"
 #include "chrome/browser/sync_file_system/drive_backend/sync_task_manager.h"
 #include "chrome/browser/sync_file_system/drive_backend/task_dependency_manager.h"
 
 namespace sync_file_system {
 namespace drive_backend {
 
 const int64 SyncTaskToken::kTestingTaskTokenID = -1;
 const int64 SyncTaskToken::kForegroundTaskTokenID = 0;
 const int64 SyncTaskToken::kMinimumBackgroundTaskTokenID = 1;
 
 // static
 scoped_ptr<SyncTaskToken> SyncTaskToken::CreateForTesting(
     const SyncStatusCallback& callback) {
   return make_scoped_ptr(new SyncTaskToken(
       base::WeakPtr<SyncTaskManager>(),
       base::ThreadTaskRunnerHandle::Get(),
       kTestingTaskTokenID,
-      scoped_ptr<TaskBlocker>(),
+      nullptr,  // task_blocker
       callback));
 }
 
 // static
 scoped_ptr<SyncTaskToken> SyncTaskToken::CreateForForegroundTask(
     const base::WeakPtr<SyncTaskManager>& manager,
     base::SequencedTaskRunner* task_runner) {
   return make_scoped_ptr(new SyncTaskToken(
       manager,
       task_runner,
       kForegroundTaskTokenID,
-      scoped_ptr<TaskBlocker>(),
+      nullptr,  // task_blocker
       SyncStatusCallback()));
 }
 
 // static
 scoped_ptr<SyncTaskToken> SyncTaskToken::CreateForBackgroundTask(
     const base::WeakPtr<SyncTaskManager>& manager,
     base::SequencedTaskRunner* task_runner,
     int64 token_id,
     scoped_ptr<TaskBlocker> task_blocker) {
   return make_scoped_ptr(new SyncTaskToken(
@@ skipping 96 matching lines @@
     const SyncStatusCallback& callback)
     : manager_(manager),
       task_runner_(task_runner),
       token_id_(token_id),
       callback_(callback),
       task_blocker_(task_blocker.Pass()) {
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system