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

webkit/browser/fileapi/file_system_backend.h

 // Copyright (c) 2012 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 WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_BACKEND_H_
 #define WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_BACKEND_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 90 matching lines @@
   // offset |offset|. |expected_modification_time| specifies the expected last
   // modification if the value is non-null, the reader will check the underlying
   // file's actual modification time to see if the file has been modified, and
   // if it does any succeeding read operations should fail with
   // ERR_UPLOAD_FILE_CHANGED error.
   // This method itself does *not* check if the given path exists and is a
   // regular file.
   virtual scoped_ptr<webkit_blob::FileStreamReader> CreateFileStreamReader(
       const FileSystemURL& url,
       int64 offset,
+      int64 length,
       const base::Time& expected_modification_time,
       FileSystemContext* context) const = 0;
 
   // Creates a new file stream writer for a given filesystem URL |url| with an
   // offset |offset|.
   // This method itself does *not* check if the given path exists and is a
   // regular file.
   virtual scoped_ptr<FileStreamWriter> CreateFileStreamWriter(
       const FileSystemURL& url,
       int64 offset,
@@ skipping 28 matching lines @@
         const std::string& extension_id) = 0;
   // Gets virtual path by known filesystem path. Returns false when filesystem
   // path is not exposed by this provider.
   virtual bool GetVirtualPath(const base::FilePath& file_system_path,
                               base::FilePath* virtual_path) = 0;
 };
 
 }  // namespace fileapi
 
 #endif  // WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_BACKEND_H_