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

content/shell/shell_download_manager_delegate.cc

 // 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.
 
 #include "content/shell/shell_download_manager_delegate.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
 #include <commdlg.h>
 #endif
@@ skipping 34 matching lines @@
   DownloadItem* download =
       download_manager_->GetActiveDownloadItem(download_id);
   DownloadStateInfo state = download->GetStateInfo();
 
   if (!state.force_file_name.empty())
     return true;
 
   FilePath generated_name = net::GenerateFileName(
       download->GetURL(),
       download->GetContentDisposition(),
-      download->GetReferrerCharset(),
+      download->GetDefaultCharset(),
       download->GetSuggestedFilename(),
       download->GetMimeType(),
       "download");
 
   // Since we have no download UI, show the user a dialog always.
   state.prompt_user_for_save_location = true;
 
   BrowserThread::PostTask(
       BrowserThread::FILE,
       FROM_HERE,
@@ skipping 66 matching lines @@
 #endif
 
   if (result.empty()) {
     download_manager_->FileSelectionCanceled(data);
   } else {
     download_manager_->FileSelected(result, data);
   }
 }
 
 }  // namespace content