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

content/browser/download/download_create_info.h

Index: content/browser/download/download_create_info.h
===================================================================
--- content/browser/download/download_create_info.h	(revision 119865)
+++ content/browser/download/download_create_info.h	(working copy)
@@ -100,9 +100,8 @@
   // The original name for a dangerous download.
   FilePath original_name;
 
-  // 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 download file save info.
   DownloadSaveInfo save_info;