[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 23 matching lines @@
 storage::AsyncFileUtil* BackendDelegate::GetAsyncFileUtil(
     storage::FileSystemType type) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK_EQ(storage::kFileSystemTypeProvided, type);
   return async_file_util_.get();
 }
 
 scoped_ptr<storage::FileStreamReader> BackendDelegate::CreateFileStreamReader(
     const storage::FileSystemURL& url,
     int64 offset,
+    int64 max_bytes_to_read,
     const base::Time& expected_modification_time,
     storage::FileSystemContext* context) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK_EQ(storage::kFileSystemTypeProvided, url.type());
 
   return scoped_ptr<storage::FileStreamReader>(new BufferingFileStreamReader(
       scoped_ptr<storage::FileStreamReader>(new FileStreamReader(
           context, url, offset, expected_modification_time)),
-      kReaderBufferSize));
+      kReaderBufferSize,
+      max_bytes_to_read));
 }
 
 scoped_ptr<storage::FileStreamWriter> BackendDelegate::CreateFileStreamWriter(
     const storage::FileSystemURL& url,
     int64 offset,
     storage::FileSystemContext* context) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK_EQ(storage::kFileSystemTypeProvided, url.type());
 
   return scoped_ptr<storage::FileStreamWriter>(
       new FileStreamWriter(url, offset));
 }
 
 storage::WatcherManager* BackendDelegate::GetWatcherManager(
     const storage::FileSystemURL& url) {
   NOTIMPLEMENTED();
   return NULL;
 }
 
 void BackendDelegate::GetRedirectURLForContents(
     const storage::FileSystemURL& url,
     const storage::URLCallback& callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK_EQ(storage::kFileSystemTypeProvided, url.type());
   callback.Run(GURL());
 }
 
 }  // namespace file_system_provider
 }  // namespace chromeos