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

chrome/browser/chromeos/fileapi/file_system_backend.h

 // Copyright 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_FILEAPI_FILE_SYSTEM_BACKEND_H_
 #define CHROME_BROWSER_CHROMEOS_FILEAPI_FILE_SYSTEM_BACKEND_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 90 matching lines @@
       const fileapi::FileSystemURL& url,
       fileapi::FileSystemContext* context,
       base::File::Error* error_code) const OVERRIDE;
   virtual bool SupportsStreaming(
       const fileapi::FileSystemURL& url) const OVERRIDE;
   virtual bool HasInplaceCopyImplementation(
       fileapi::FileSystemType type) const OVERRIDE;
   virtual scoped_ptr<webkit_blob::FileStreamReader> CreateFileStreamReader(
       const fileapi::FileSystemURL& path,
       int64 offset,
+      int64 length,
       const base::Time& expected_modification_time,
       fileapi::FileSystemContext* context) const OVERRIDE;
   virtual scoped_ptr<fileapi::FileStreamWriter> CreateFileStreamWriter(
       const fileapi::FileSystemURL& url,
       int64 offset,
       fileapi::FileSystemContext* context) const OVERRIDE;
   virtual fileapi::FileSystemQuotaUtil* GetQuotaUtil() OVERRIDE;
 
   // fileapi::ExternalFileSystemBackend overrides.
   virtual bool IsAccessAllowed(const fileapi::FileSystemURL& url)
@@ skipping 39 matching lines @@
   // Globally visible mount points. System MountPonts instance should outlive
   // all FileSystemBackend instances, so raw pointer is safe.
   fileapi::ExternalMountPoints* system_mount_points_;
 
   DISALLOW_COPY_AND_ASSIGN(FileSystemBackend);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_FILEAPI_FILE_SYSTEM_BACKEND_H_