[fsp] Add FileStreamReader for the reading operation.

chrome/browser/chromeos/file_system_provider/operations/read_file.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 "chrome/browser/chromeos/file_system_provider/operations/read_file.h"
 
 #include <limits>
 #include <string>
 
 #include "chrome/common/extensions/api/file_system_provider.h"
@@ skipping 36 matching lines @@
     int file_handle,
     net::IOBuffer* buffer,
     int64 offset,
     int length,
     const ProvidedFileSystemInterface::ReadChunkReceivedCallback& callback)
     : Operation(event_router, file_system_info),
       file_handle_(file_handle),
       buffer_(buffer),
       offset_(offset),
       length_(length),
-      current_offset_(offset),
+      current_offset_(0),
       callback_(callback) {
 }
 
 ReadFile::~ReadFile() {
 }
 
 bool ReadFile::Execute(int request_id) {
   scoped_ptr<base::ListValue> values(new base::ListValue);
   values->AppendInteger(file_handle_);
   values->AppendDouble(offset_);
@@ skipping 16 matching lines @@
   callback_.Run(copy_result, has_next, base::File::FILE_OK);
 }
 
 void ReadFile::OnError(int /* request_id */, base::File::Error error) {
   callback_.Run(0 /* chunk_length */, false /* has_next */, error);
 }
 
 }  // namespace operations
 }  // namespace file_system_provider
 }  // namespace chromeos