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

chrome/browser/chromeos/fileapi/file_system_backend.cc

Index: chrome/browser/chromeos/fileapi/file_system_backend.cc
diff --git a/chrome/browser/chromeos/fileapi/file_system_backend.cc b/chrome/browser/chromeos/fileapi/file_system_backend.cc
index f5e80fbf52239336ccd7f2985a825174f14f8534..d2ad6faff8773fdd7d94d67b2a82372711a5bc8d 100644
--- a/chrome/browser/chromeos/fileapi/file_system_backend.cc
+++ b/chrome/browser/chromeos/fileapi/file_system_backend.cc
@@ -310,7 +310,8 @@
   DCHECK(url.type() == fileapi::kFileSystemTypeNativeLocal);
   return scoped_ptr<fileapi::FileStreamWriter>(
       fileapi::FileStreamWriter::CreateForLocalFile(
-          context->default_file_task_runner(), url.path(), offset));
+          context->default_file_task_runner(), url.path(), offset,
+          fileapi::FileStreamWriter::OPEN_EXISTING_FILE));
 }
 
 bool FileSystemBackend::GetVirtualPath(