[SyncFS] Use nullptr for scoped_ptr initialization

chrome/browser/sync_file_system/drive_backend/fake_sync_worker.cc

Index: chrome/browser/sync_file_system/drive_backend/fake_sync_worker.cc
diff --git a/chrome/browser/sync_file_system/drive_backend/fake_sync_worker.cc b/chrome/browser/sync_file_system/drive_backend/fake_sync_worker.cc
index 6584a08395d7db24209c205c4ef9df599cd0dc33..4dbcce84a3090ebff652ed1abf2f31a2bff4e1ca 100644
--- a/chrome/browser/sync_file_system/drive_backend/fake_sync_worker.cc
+++ b/chrome/browser/sync_file_system/drive_backend/fake_sync_worker.cc
@@ -110,12 +110,12 @@ void FakeSyncWorker::GetOriginStatusMap(
 
 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) {