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

chrome/browser/chromeos/file_system_provider/fileapi/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/file_system_provider/fileapi/backend_delegate.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/chromeos/file_system_provider/fileapi/buffering_file_stream_reader.h"
 #include "chrome/browser/chromeos/file_system_provider/fileapi/file_stream_reader.h"
 #include "chrome/browser/chromeos/file_system_provider/fileapi/file_stream_writer.h"
@@ skipping 24 matching lines @@
     fileapi::FileSystemType type) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK_EQ(fileapi::kFileSystemTypeProvided, type);
   return async_file_util_.get();
 }
 
 scoped_ptr<webkit_blob::FileStreamReader>
 BackendDelegate::CreateFileStreamReader(
     const fileapi::FileSystemURL& url,
     int64 offset,
+    int64 length,
     const base::Time& expected_modification_time,
     fileapi::FileSystemContext* context) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK_EQ(fileapi::kFileSystemTypeProvided, url.type());
 
   return scoped_ptr<webkit_blob::FileStreamReader>(
       new BufferingFileStreamReader(
           scoped_ptr<webkit_blob::FileStreamReader>(new FileStreamReader(
               context, url, offset, expected_modification_time)),
-          kReaderBufferSize));
+          kReaderBufferSize,
+          length));
 }
 
 scoped_ptr<fileapi::FileStreamWriter> BackendDelegate::CreateFileStreamWriter(
     const fileapi::FileSystemURL& url,
     int64 offset,
     fileapi::FileSystemContext* context) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK_EQ(fileapi::kFileSystemTypeProvided, url.type());
 
   return scoped_ptr<fileapi::FileStreamWriter>(
       new FileStreamWriter(url, offset));
 }
 
 }  // namespace file_system_provider
 }  // namespace chromeos