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

chrome/browser/chromeos/fileapi/file_system_backend.cc

 // 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.
 
 #include "chrome/browser/chromeos/fileapi/file_system_backend.h"
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/stringprintf.h"
 #include "chrome/browser/chromeos/fileapi/file_access_permissions.h"
@@ skipping 296 matching lines @@
       return false;
     default:
       NOTREACHED();
   }
   return true;
 }
 
 scoped_ptr<storage::FileStreamReader> FileSystemBackend::CreateFileStreamReader(
     const storage::FileSystemURL& url,
     int64 offset,
+    int64 length,
     const base::Time& expected_modification_time,
     storage::FileSystemContext* context) const {
   DCHECK(url.is_valid());
 
   if (!IsAccessAllowed(url))
     return scoped_ptr<storage::FileStreamReader>();
 
   switch (url.type()) {
     case storage::kFileSystemTypeDrive:
       return drive_delegate_->CreateFileStreamReader(
-          url, offset, expected_modification_time, context);
+          url, offset, length, expected_modification_time, context);
     case storage::kFileSystemTypeProvided:
       return file_system_provider_delegate_->CreateFileStreamReader(
-          url, offset, expected_modification_time, context);
+          url, offset, length, expected_modification_time, context);
     case storage::kFileSystemTypeNativeLocal:
     case storage::kFileSystemTypeRestrictedNativeLocal:
       return scoped_ptr<storage::FileStreamReader>(
           storage::FileStreamReader::CreateForFileSystemFile(
               context, url, offset, expected_modification_time));
     case storage::kFileSystemTypeDeviceMediaAsFileStorage:
       return mtp_delegate_->CreateFileStreamReader(
-          url, offset, expected_modification_time, context);
+          url, offset, length, expected_modification_time, context);
     default:
       NOTREACHED();
   }
   return scoped_ptr<storage::FileStreamReader>();
 }
 
 scoped_ptr<storage::FileStreamWriter> FileSystemBackend::CreateFileStreamWriter(
     const storage::FileSystemURL& url,
     int64 offset,
     storage::FileSystemContext* context) const {
@@ skipping 27 matching lines @@
 }
 
 bool FileSystemBackend::GetVirtualPath(
     const base::FilePath& filesystem_path,
     base::FilePath* virtual_path) {
   return mount_points_->GetVirtualPath(filesystem_path, virtual_path) ||
          system_mount_points_->GetVirtualPath(filesystem_path, virtual_path);
 }
 
 }  // namespace chromeos