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

content/browser/download/download_manager_impl_unittest.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 <set>
 #include <string>
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 96 matching lines @@
 
   void set_prompt_user_for_save_location(bool value) {
     prompt_user_for_save_location_ = value;
   }
 
   virtual bool ShouldStartDownload(int32 download_id) OVERRIDE {
     DownloadItem* item = download_manager_->GetActiveDownloadItem(download_id);
     DownloadStateInfo state = item->GetStateInfo();
     FilePath path = net::GenerateFileName(item->GetURL(),
                                           item->GetContentDisposition(),
-                                          item->GetReferrerCharset(),
+                                          item->GetDefaultCharset(),
                                           item->GetSuggestedFilename(),
                                           item->GetMimeType(),
                                           std::string());
     if (!ShouldOpenFileBasedOnExtension(path) && prompt_user_for_save_location_)
       state.prompt_user_for_save_location = true;
     item->SetFileCheckResults(state);
     return true;
   }
 
   virtual FilePath GetIntermediatePath(
@@ skipping 1175 matching lines @@
   EXPECT_FALSE(observer->hit_state(DownloadItem::INTERRUPTED));
   EXPECT_TRUE(observer->hit_state(DownloadItem::COMPLETE));
   EXPECT_FALSE(observer->hit_state(DownloadItem::REMOVING));
   EXPECT_TRUE(observer->was_updated());
   EXPECT_FALSE(observer->was_opened());
   EXPECT_TRUE(download->GetFileExternallyRemoved());
   EXPECT_EQ(DownloadItem::COMPLETE, download->GetState());
 
   EXPECT_FALSE(file_util::PathExists(new_path));
 }