MTP Streaming: Optimize block reading

chrome/browser/media_galleries/linux/mtp_device_task_helper.h

Index: chrome/browser/media_galleries/linux/mtp_device_task_helper.h
diff --git a/chrome/browser/media_galleries/linux/mtp_device_task_helper.h b/chrome/browser/media_galleries/linux/mtp_device_task_helper.h
index 9c1a8f6d8fd0634f9473c536076cd58b65ff616b..9b991b3202e7eef30f6e192d69bc9a2a1550632c 100644
--- a/chrome/browser/media_galleries/linux/mtp_device_task_helper.h
+++ b/chrome/browser/media_galleries/linux/mtp_device_task_helper.h
@@ -32,6 +32,8 @@ class MTPDeviceTaskHelper {
   typedef MTPDeviceAsyncDelegate::GetFileInfoSuccessCallback
       GetFileInfoSuccessCallback;
 
+  typedef base::Callback<void(int)> ReadBytesSuccessCallback;
+
   typedef base::Callback<void(const fileapi::AsyncFileUtil::EntryList&)>
       ReadDirectorySuccessCallback;
 
@@ -89,10 +91,15 @@ class MTPDeviceTaskHelper {
 
   // Dispatches the read bytes request to the MediaTransferProtocolManager.
   //
-  // |request| contains details about the byte request including the file path,
-  // byte range, and the callbacks. The callbacks specified within |request| are
-  // called on the IO thread to notify the caller about success or failure.
-  void ReadBytes(const MTPDeviceAsyncDelegate::ReadBytesRequest& request);
+  // |success_callback| is invoked on the IO thread to notify the caller about
+  // the number of bytes read.
+  //
+  // If there is an error, |error_callback| is invoked on the IO thread to
+  // notify the caller about the file error.
+  void ReadBytes(const std::string& device_file_relative_path,
+                 net::IOBuffer* buf, int64 offset, int buf_len,
+                 const ReadBytesSuccessCallback& success_callback,
+                 const ErrorCallback& error_callback);
 
   // Dispatches the CloseStorage request to the MediaTransferProtocolManager.
   void CloseStorage() const;
@@ -139,15 +146,16 @@ class MTPDeviceTaskHelper {
 
   // 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 no error, |error| is set to false, the buffer |buf| is written
+  // to, and |success_callback| 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.
+  // If there is an error, |error| is set to true, |buf| is untouched, and
+  // |error_callback| is invoked on the IO thread to notify the caller.
   void OnDidReadBytes(
-      const MTPDeviceAsyncDelegate::ReadBytesRequest& request,
+      net::IOBuffer* buf, int buf_len,
+      const ReadBytesSuccessCallback& success_callback,
+      const ErrorCallback& error_callback,
       const std::string& data,
       bool error) const;