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

content/browser/download/download_item_impl.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_ITEM_IMPL_H_
 #define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_ITEM_IMPL_H_
 #pragma once
 
 #include <string>
 
@@ skipping 135 matching lines @@
   virtual const FilePath& GetFullPath() const OVERRIDE;
   virtual void SetPathUniquifier(int uniquifier) OVERRIDE;
   virtual const GURL& GetURL() const OVERRIDE;
   virtual const std::vector<GURL>& GetUrlChain() const OVERRIDE;
   virtual const GURL& GetOriginalUrl() const OVERRIDE;
   virtual const GURL& GetReferrerUrl() const OVERRIDE;
   virtual std::string GetSuggestedFilename() const OVERRIDE;
   virtual std::string GetContentDisposition() const OVERRIDE;
   virtual std::string GetMimeType() const OVERRIDE;
   virtual std::string GetOriginalMimeType() const OVERRIDE;
-  virtual std::string GetReferrerCharset() const OVERRIDE;
+  virtual std::string GetDefaultCharset() const OVERRIDE;
   virtual std::string GetRemoteAddress() const OVERRIDE;
   virtual int64 GetTotalBytes() const OVERRIDE;
   virtual void SetTotalBytes(int64 total_bytes) OVERRIDE;
   virtual const std::string& GetHash() const OVERRIDE;
   virtual int64 GetReceivedBytes() const OVERRIDE;
   virtual const std::string& GetHashState() const OVERRIDE;
   virtual int32 GetId() const OVERRIDE;
   virtual content::DownloadId GetGlobalId() const OVERRIDE;
   virtual base::Time GetStartTime() const OVERRIDE;
   virtual base::Time GetEndTime() const OVERRIDE;
@@ skipping 97 matching lines @@
   std::string content_disposition_;
 
   // Mime-type from the header.  Subject to change.
   std::string mime_type_;
 
   // The value of the content type header sent with the downloaded item.  It
   // may be different from |mime_type_|, which may be set based on heuristics
   // which may look at the file extension and first few bytes of the file.
   std::string original_mime_type_;
 
-  // 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 remote IP address where the download was fetched from.  Copied from
   // DownloadCreateInfo::remote_address.
   std::string remote_address_;
 
   // Total bytes expected.
   int64 total_bytes_;
 
   // Current received bytes.
   int64 received_bytes_;
@@ skipping 81 matching lines @@
   bool delegate_delayed_complete_;
 
   // External Data storage.  All objects in the store
   // are owned by the DownloadItemImpl.
   std::map<const void*, ExternalData*> external_data_map_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadItemImpl);
 };
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_ITEM_IMPL_H_