Revert of Revert of Add a parameter to FileStreamWriter::CreateForLocalFile to allow creating new

chrome/browser/media_galleries/fileapi/media_file_system_backend.cc

 // Copyright (c) 2013 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/media_galleries/fileapi/media_file_system_backend.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
@@ skipping 198 matching lines @@
 }
 
 scoped_ptr<fileapi::FileStreamWriter>
 MediaFileSystemBackend::CreateFileStreamWriter(
     const FileSystemURL& url,
     int64 offset,
     FileSystemContext* context) const {
   return scoped_ptr<fileapi::FileStreamWriter>(
       fileapi::FileStreamWriter::CreateForLocalFile(
           context->default_file_task_runner(),
-          url.path(), offset));
+          url.path(),
+          offset,
+          fileapi::FileStreamWriter::OPEN_EXISTING_FILE));
 }
 
 fileapi::FileSystemQuotaUtil*
 MediaFileSystemBackend::GetQuotaUtil() {
   // No quota support.
   return NULL;
 }