Media Galleries: Access MTP devices by file ids rather than file paths.

chrome/browser/media_galleries/fileapi/mtp_device_async_delegate.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/media_galleries/fileapi/mtp_device_async_delegate.h"
 
 #include "net/base/io_buffer.h"
 
 MTPDeviceAsyncDelegate::ReadBytesRequest::ReadBytesRequest(
-    const std::string& device_file_relative_path,
-    net::IOBuffer* buf, int64 offset, int buf_len,
+    uint32 file_id, net::IOBuffer* buf, int64 offset, int buf_len,
     const ReadBytesSuccessCallback& success_callback,
     const ErrorCallback& error_callback)
-    : device_file_relative_path(device_file_relative_path),
+    : file_id(file_id),
       buf(buf),
       offset(offset),
       buf_len(buf_len),
       success_callback(success_callback),
       error_callback(error_callback) {
 }
 
 MTPDeviceAsyncDelegate::ReadBytesRequest::~ReadBytesRequest() {}