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

net/http/http_content_disposition.h

 // 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.
 
 #ifndef NET_HTTP_HTTP_CONTENT_DISPOSITION_H_
 #define NET_HTTP_HTTP_CONTENT_DISPOSITION_H_
 #pragma once
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "net/base/net_export.h"
 
 namespace net {
 
 class NET_EXPORT HttpContentDisposition {
  public:
   enum Type {
     INLINE,
     ATTACHMENT,
   };
 
   HttpContentDisposition(const std::string& header,
-                         const std::string& referrer_charset);
+                         const std::string& default_charset);
   ~HttpContentDisposition();
 
   bool is_attachment() const { return type() == ATTACHMENT; }
 
   Type type() const { return type_; }
   const std::string& filename() const { return filename_; }
 
  private:
-  void Parse(const std::string& header, const std::string& referrer_charset);
+  void Parse(const std::string& header, const std::string& default_charset);
   std::string::const_iterator ConsumeDispositionType(
       std::string::const_iterator begin, std::string::const_iterator end);
 
   Type type_;
   std::string filename_;
 
   DISALLOW_COPY_AND_ASSIGN(HttpContentDisposition);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_CONTENT_DISPOSITION_H_