[fsp] Improve performance for reading small chunks of data.

chrome/browser/chromeos/drive/fileapi/file_system_backend_delegate.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/chromeos/drive/fileapi/file_system_backend_delegate.h"
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/chromeos/drive/file_system_util.h"
@@ skipping 23 matching lines @@
     fileapi::FileSystemType type) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   DCHECK_EQ(fileapi::kFileSystemTypeDrive, type);
   return async_file_util_.get();
 }
 
 scoped_ptr<webkit_blob::FileStreamReader>
 FileSystemBackendDelegate::CreateFileStreamReader(
     const fileapi::FileSystemURL& url,
     int64 offset,
+    int64 length,
     const base::Time& expected_modification_time,
     fileapi::FileSystemContext* context) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   DCHECK_EQ(fileapi::kFileSystemTypeDrive, url.type());
 
   base::FilePath file_path = util::ExtractDrivePathFromFileSystemUrl(url);
   if (file_path.empty())
     return scoped_ptr<webkit_blob::FileStreamReader>();
 
   return scoped_ptr<webkit_blob::FileStreamReader>(
@@ skipping 16 matching lines @@
   if (file_path.empty() || util::HasHostedDocumentExtension(file_path))
     return scoped_ptr<fileapi::FileStreamWriter>();
 
   return scoped_ptr<fileapi::FileStreamWriter>(
       new internal::WebkitFileStreamWriterImpl(
           base::Bind(&fileapi_internal::GetFileSystemFromUrl, url),
           context->default_file_task_runner(),file_path, offset));
 }
 
 }  // namespace drive