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

content/browser/download/download_item_impl.cc

Index: content/browser/download/download_item_impl.cc
===================================================================
--- content/browser/download/download_item_impl.cc	(revision 119865)
+++ content/browser/download/download_item_impl.cc	(working copy)
@@ -212,7 +212,7 @@
       content_disposition_(info.content_disposition),
       mime_type_(info.mime_type),
       original_mime_type_(info.original_mime_type),
-      referrer_charset_(info.referrer_charset),
+      default_charset_(info.default_charset),
       remote_address_(info.remote_address),
       total_bytes_(info.total_bytes),
       received_bytes_(0),
@@ -929,8 +929,8 @@
 std::string DownloadItemImpl::GetOriginalMimeType() const {
   return original_mime_type_;
 }
-std::string DownloadItemImpl::GetReferrerCharset() const {
-  return referrer_charset_;
+std::string DownloadItemImpl::GetDefaultCharset() const {
+  return default_charset_;
 }
 std::string DownloadItemImpl::GetRemoteAddress() const {
   return remote_address_;