[Downloads] Rework how hashes are calculated for download files.

content/public/browser/download_save_info.cc

 // Copyright (c) 2012 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/public/browser/download_save_info.h"
 
 namespace content {
 
 DownloadSaveInfo::DownloadSaveInfo()
     : offset(0), prompt_for_save_location(false) {
 }
 
 DownloadSaveInfo::~DownloadSaveInfo() {
 }
 
+DownloadSaveInfo::DownloadSaveInfo(DownloadSaveInfo&& that)
+    : file_path(std::move(that.file_path)),
+      suggested_name(std::move(that.suggested_name)),
+      file(std::move(that.file)),
+      offset(that.offset),
+      hash_state(std::move(that.hash_state)),
+      prefix_hash(std::move(that.prefix_hash)),
+      prompt_for_save_location(that.prompt_for_save_location) {}
+
 }  // namespace content