[SyncFS] Use nullptr for scoped_ptr initialization

chrome/browser/sync_file_system/mock_remote_file_sync_service.cc

 // Copyright (c) 2012 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/mock_remote_file_sync_service.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/location.h"
@@ skipping 27 matching lines @@
       .WillByDefault(Return(&mock_local_change_processor_));
   ON_CALL(*this, GetCurrentState())
       .WillByDefault(Invoke(this, &self::GetCurrentStateStub));
 }
 
 MockRemoteFileSyncService::~MockRemoteFileSyncService() {
 }
 
 void MockRemoteFileSyncService::DumpFiles(const GURL& origin,
                                           const ListCallback& callback) {
-  callback.Run(scoped_ptr<base::ListValue>());
+  callback.Run(nullptr);
 }
 
 void MockRemoteFileSyncService::DumpDatabase(const ListCallback& callback) {
-  callback.Run(scoped_ptr<base::ListValue>());
+  callback.Run(nullptr);
 }
 
 void MockRemoteFileSyncService::SetServiceState(RemoteServiceState state) {
   state_ = state;
 }
 
 void MockRemoteFileSyncService::NotifyRemoteChangeQueueUpdated(
     int64 pending_changes) {
   FOR_EACH_OBSERVER(Observer, service_observers_,
                     OnRemoteChangeQueueUpdated(pending_changes));
@@ skipping 48 matching lines @@
       FROM_HERE,
       base::Bind(
           callback, SYNC_STATUS_NO_CHANGE_TO_SYNC, storage::FileSystemURL()));
 }
 
 RemoteServiceState MockRemoteFileSyncService::GetCurrentStateStub() const {
   return state_;
 }
 
 }  // namespace sync_file_system