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

content/browser/download/download_item_impl.h

Index: content/browser/download/download_item_impl.h
===================================================================
--- content/browser/download/download_item_impl.h	(revision 119865)
+++ content/browser/download/download_item_impl.h	(working copy)
@@ -153,7 +153,7 @@
   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;
@@ -271,9 +271,8 @@
   // 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.