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

content/browser/fileapi/upload_file_system_file_element_reader.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 "content/browser/fileapi/upload_file_system_file_element_reader.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
+#include "base/numerics/safe_conversions.h"
 #include "net/base/net_errors.h"
 #include "webkit/browser/blob/file_stream_reader.h"
 #include "webkit/browser/fileapi/file_system_context.h"
 #include "webkit/browser/fileapi/file_system_url.h"
 
 namespace content {
 
 UploadFileSystemFileElementReader::UploadFileSystemFileElementReader(
     storage::FileSystemContext* file_system_context,
     const GURL& url,
@@ skipping 14 matching lines @@
 }
 
 int UploadFileSystemFileElementReader::Init(
     const net::CompletionCallback& callback) {
   // Reset states.
   weak_ptr_factory_.InvalidateWeakPtrs();
   stream_length_ = 0;
   position_ = 0;
 
   // Initialize the stream reader and the length.
-  stream_reader_ =
-      file_system_context_->CreateFileStreamReader(
-          file_system_context_->CrackURL(url_),
-          range_offset_,
-          expected_modification_time_);
+  stream_reader_ = file_system_context_->CreateFileStreamReader(
+      file_system_context_->CrackURL(url_),
+      range_offset_,
+      base::checked_cast<int64>(range_length_),
+      expected_modification_time_);
   DCHECK(stream_reader_);
 
   const int64 result = stream_reader_->GetLength(
       base::Bind(&UploadFileSystemFileElementReader::OnGetLength,
                  weak_ptr_factory_.GetWeakPtr(),
                  callback));
   if (result >= 0) {
     stream_length_ = result;
     return net::OK;
   }
@@ skipping 49 matching lines @@
     int result) {
   if (result > 0) {
     position_ += result;
     DCHECK_LE(position_, GetContentLength());
   }
   if (!callback.is_null())
     callback.Run(result);
 }
 
 }  // namespace content