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

net/url_request/url_request_context.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.
 
 // This class represents contextual information (cookies, cache, etc.)
 // that's useful when processing resource requests.
 // The class is reference-counted so that it can be cleaned up after any
 // requests that are using it have been completed.
 
 #ifndef NET_URL_REQUEST_URL_REQUEST_CONTEXT_H_
@@ skipping 159 matching lines @@
   const std::string& accept_language() const { return accept_language_; }
   void set_accept_language(const std::string& accept_language) {
     accept_language_ = accept_language;
   }
 
   // Gets the UA string to use for the given URL.  Pass an invalid URL (such as
   // GURL()) to get the default UA string.  Subclasses should override this
   // method to provide a UA string.
   virtual const std::string& GetUserAgent(const GURL& url) const;
 
-  // In general, referrer_charset is not known when URLRequestContext is
-  // constructed. So, we need a setter.
-  const std::string& referrer_charset() const { return referrer_charset_; }
-  void set_referrer_charset(const std::string& charset) {
-    referrer_charset_ = charset;
+  const std::string& default_charset() const { return default_charset_; }
+  void set_default_charset(const std::string& charset) {
+    default_charset_ = charset;
   }
 
   const URLRequestJobFactory* job_factory() const { return job_factory_; }
   void set_job_factory(const URLRequestJobFactory* job_factory) {
     job_factory_ = job_factory;
   }
 
  protected:
   friend class base::RefCountedThreadSafe<URLRequestContext>;
 
@@ skipping 17 matching lines @@
   HttpAuthHandlerFactory* http_auth_handler_factory_;
   ProxyService* proxy_service_;
   scoped_refptr<SSLConfigService> ssl_config_service_;
   NetworkDelegate* network_delegate_;
   HttpServerProperties* http_server_properties_;
   scoped_refptr<CookieStore> cookie_store_;
   TransportSecurityState* transport_security_state_;
   scoped_ptr<FtpAuthCache> ftp_auth_cache_;
   std::string accept_language_;
   std::string accept_charset_;
-  // The charset of the referrer where this request comes from. It's not
-  // used in communication with a server but is used to construct a suggested
-  // filename for file download.
-  std::string referrer_charset_;
+  // The user's default charset. It's not used in communication with a server
+  // but is used to construct a suggested filename for file download.
+  std::string default_charset_;
   HttpTransactionFactory* http_transaction_factory_;
   FtpTransactionFactory* ftp_transaction_factory_;
   const URLRequestJobFactory* job_factory_;
 
   // ---------------------------------------------------------------------------
   // Important: When adding any new members below, consider whether they need to
   // be added to CopyFrom.
   // ---------------------------------------------------------------------------
 
   DISALLOW_COPY_AND_ASSIGN(URLRequestContext);
 };
 
 }  // namespace net
 
 #endif  // NET_URL_REQUEST_URL_REQUEST_CONTEXT_H_