[SyncFS] Use nullptr for scoped_ptr initialization

chrome/browser/sync_file_system/drive_backend/fake_sync_worker.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/fake_sync_worker.h"
 
 #include "base/values.h"
 #include "chrome/browser/sync_file_system/drive_backend/drive_backend_constants.h"
 #include "chrome/browser/sync_file_system/drive_backend/sync_engine_context.h"
 #include "chrome/browser/sync_file_system/sync_status_code.h"
@@ skipping 92 matching lines @@
     default:
       (*status_map)[itr->first] = "Unknown";
       break;
     }
   }
   callback.Run(status_map.Pass());
 }
 
 scoped_ptr<base::ListValue> FakeSyncWorker::DumpFiles(const GURL& origin) {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
-  return scoped_ptr<base::ListValue>();
+  return nullptr;
 }
 
 scoped_ptr<base::ListValue> FakeSyncWorker::DumpDatabase() {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
-  return scoped_ptr<base::ListValue>();
+  return nullptr;
 }
 
 void FakeSyncWorker::SetSyncEnabled(bool enabled) {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
   sync_enabled_ = enabled;
 
   if (enabled)
     UpdateServiceState(REMOTE_SERVICE_OK, "Set FakeSyncWorker enabled.");
   else
     UpdateServiceState(REMOTE_SERVICE_DISABLED, "Disabled FakeSyncWorker.");
@@ skipping 41 matching lines @@
                                         const std::string& description) {
   DCHECK(sequence_checker_.CalledOnValidSequencedThread());
 
   FOR_EACH_OBSERVER(
       Observer, observers_,
       UpdateServiceState(state, description));
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system