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

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 309 matching lines @@
          type == fileapi::kFileSystemTypeItunes ||
          type == fileapi::kFileSystemTypePicasa ||
          type == fileapi::kFileSystemTypeIphoto);
   return true;
 }
 
 scoped_ptr<webkit_blob::FileStreamReader>
 MediaFileSystemBackend::CreateFileStreamReader(
     const FileSystemURL& url,
     int64 offset,
+    int64 length,
     const base::Time& expected_modification_time,
     FileSystemContext* context) const {
   if (url.type() == fileapi::kFileSystemTypeDeviceMedia) {
     DCHECK(device_media_async_file_util_);
     scoped_ptr<webkit_blob::FileStreamReader> reader =
         device_media_async_file_util_->GetFileStreamReader(
             url, offset, expected_modification_time, context);
     DCHECK(reader);
     return reader.Pass();
   }
@@ skipping 15 matching lines @@
           url.path(),
           offset,
           fileapi::FileStreamWriter::OPEN_EXISTING_FILE));
 }
 
 fileapi::FileSystemQuotaUtil*
 MediaFileSystemBackend::GetQuotaUtil() {
   // No quota support.
   return NULL;
 }