MTP Streaming: Optimize block reading

chrome/browser/media_galleries/linux/mtp_device_task_helper.cc

Index: chrome/browser/media_galleries/linux/mtp_device_task_helper.cc
diff --git a/chrome/browser/media_galleries/linux/mtp_device_task_helper.cc b/chrome/browser/media_galleries/linux/mtp_device_task_helper.cc
index a1546c747c32e48671d8b9c5d656744ca45ab27d..a1ca0fef70258e41d584924f6912af35f3f0274c 100644
--- a/chrome/browser/media_galleries/linux/mtp_device_task_helper.cc
+++ b/chrome/browser/media_galleries/linux/mtp_device_task_helper.cc
@@ -109,20 +109,23 @@ void MTPDeviceTaskHelper::WriteDataIntoSnapshotFile(
 }
 
 void MTPDeviceTaskHelper::ReadBytes(
-    const MTPDeviceAsyncDelegate::ReadBytesRequest& request) {
+    const std::string& device_file_relative_path,
+    net::IOBuffer* buf, int64 offset, int buf_len,
+    const ReadBytesSuccessCallback& success_callback,
+    const ErrorCallback& error_callback) {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
   if (device_handle_.empty()) {
-    return HandleDeviceError(request.error_callback,
-                             base::File::FILE_ERROR_FAILED);
+    return HandleDeviceError(error_callback, base::File::FILE_ERROR_FAILED);
   }
 
   GetMediaTransferProtocolManager()->ReadFileChunkByPath(
       device_handle_,
-      request.device_file_relative_path,
-      base::checked_cast<uint32>(request.offset),
-      base::checked_cast<uint32>(request.buf_len),
+      device_file_relative_path,
+      base::checked_cast<uint32>(offset),
+      base::checked_cast<uint32>(buf_len),
       base::Bind(&MTPDeviceTaskHelper::OnDidReadBytes,
-                 weak_ptr_factory_.GetWeakPtr(), request));
+                 weak_ptr_factory_.GetWeakPtr(), make_scoped_refptr(buf),
+                 buf_len, success_callback, error_callback));
 }
 
 void MTPDeviceTaskHelper::CloseStorage() const {
@@ -196,22 +199,22 @@ void MTPDeviceTaskHelper::OnDidReadDirectoryByPath(
 }
 
 void MTPDeviceTaskHelper::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 {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
   if (error) {
-    return HandleDeviceError(request.error_callback,
-                             base::File::FILE_ERROR_FAILED);
+    return HandleDeviceError(error_callback, base::File::FILE_ERROR_FAILED);
   }
 
-  CHECK_LE(base::checked_cast<int>(data.length()), request.buf_len);
-  std::copy(data.begin(), data.end(), request.buf->data());
+  CHECK_LE(base::checked_cast<int>(data.length()), buf_len);
+  std::copy(data.begin(), data.end(), buf->data());
 
   content::BrowserThread::PostTask(content::BrowserThread::IO,
                                    FROM_HERE,
-                                   base::Bind(request.success_callback,
-                                              data.length()));
+                                   base::Bind(success_callback, data.length()));
 }
 
 void MTPDeviceTaskHelper::HandleDeviceError(