referrer_charset is a lie. It's really the user's default_charset.

content/browser/download/download_create_info.h

 // Copyright (c) 2011 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.
 
 #ifndef CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_CREATE_INFO_H_
 #define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_CREATE_INFO_H_
 #pragma once
 
 #include <string>
 #include <vector>
@@ skipping 82 matching lines @@
 
   // True if we should display the 'save as...' UI and prompt the user
   // for the download location.
   // False if the UI should be suppressed and the download performed to the
   // default location.
   bool prompt_user_for_save_location;
 
   // The original name for a dangerous download.
   FilePath original_name;
 
-  // The charset of the referring page where the download request comes from.
-  // It's used to construct a suggested filename.
-  std::string referrer_charset;
+  // The user's default charset.  It's used to construct a suggested filename.
+  std::string default_charset;
 
   // The download file save info.
   DownloadSaveInfo save_info;
 
   // The remote IP address where the download was fetched from.  Copied from
   // UrlRequest::GetSocketAddress().
   std::string remote_address;
 };
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_CREATE_INFO_H_