MTP Streaming: Optimize block reading

chrome/browser/media_galleries/linux/mtp_device_task_helper.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_MEDIA_GALLERIES_LINUX_MTP_DEVICE_TASK_HELPER_H_
 #define CHROME_BROWSER_MEDIA_GALLERIES_LINUX_MTP_DEVICE_TASK_HELPER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 119 matching lines @@
   // to notify the caller.
   //
   // If there is an error, |error| is set to true, |file_entries| is empty
   // and |error_callback| is invoked on the IO thread to notify the caller.
   void OnDidReadDirectoryByPath(
       const ReadDirectorySuccessCallback& success_callback,
       const ErrorCallback& error_callback,
       const std::vector<MtpFileEntry>& file_entries,
       bool error) const;
 
+  // Intermediate step to finish a ReadBytes request.
+  void OnGetFileInfoToReadBytes(
+      const MTPDeviceAsyncDelegate::ReadBytesRequest& request,
+      const MtpFileEntry& file_entry,
+      bool error);
+
   // Query callback for ReadBytes();
   //
   // If there is no error, |error| is set to false, the buffer within |request|
   // is written to, and the success callback within |request| is invoked on the
   // IO thread to notify the caller.
   //
   // If there is an error, |error| is set to true, the buffer within |request|
   // is untouched, and the error callback within |request| is invoked on the
   // IO thread to notify the caller.
   void OnDidReadBytes(
       const MTPDeviceAsyncDelegate::ReadBytesRequest& request,
+      const base::File::Info& file_info,
       const std::string& data,
       bool error) const;
 
   // Called when the device is uninitialized.
   //
   // Runs |error_callback| on the IO thread to notify the caller about the
   // device |error|.
   void HandleDeviceError(const ErrorCallback& error_callback,
                          base::File::Error error) const;
 
   // Handle to communicate with the MTP device.
   std::string device_handle_;
 
   // Used to handle WriteDataInfoSnapshotFile request.
   scoped_ptr<MTPReadFileWorker> read_file_worker_;
 
   // For callbacks that may run after destruction.
   base::WeakPtrFactory<MTPDeviceTaskHelper> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MTPDeviceTaskHelper);
 };
 
 #endif  // CHROME_BROWSER_MEDIA_GALLERIES_LINUX_MTP_DEVICE_TASK_HELPER_H_