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

net/url_request/url_request_context.cc

Index: net/url_request/url_request_context.cc
===================================================================
--- net/url_request/url_request_context.cc	(revision 119865)
+++ net/url_request/url_request_context.cc	(working copy)
@@ -48,7 +48,7 @@
   // FTPAuthCache is unique per context.
   set_accept_language(other->accept_language());
   set_accept_charset(other->accept_charset());
-  set_referrer_charset(other->referrer_charset());
+  set_default_charset(other->default_charset());
   set_http_transaction_factory(other->http_transaction_factory());
   set_ftp_transaction_factory(other->ftp_transaction_factory());
   set_job_factory(other->job_factory());