Revert of Move JoinString to the base namespace

google_apis/gaia/gaia_auth_util.cc

Index: google_apis/gaia/gaia_auth_util.cc
diff --git a/google_apis/gaia/gaia_auth_util.cc b/google_apis/gaia/gaia_auth_util.cc
index 5464da6b141df89db038e559c9b4df7f37f513e1..e9ec5454dda76cf34b4895f2f81b843dc6b6c586 100644
--- a/google_apis/gaia/gaia_auth_util.cc
+++ b/google_apis/gaia/gaia_auth_util.cc
@@ -36,8 +36,7 @@
       base::RemoveChars(parts[0], ".", &parts[0]);
   }
 
-  std::string new_email = base::StringToLowerASCII(
-      base::JoinString(parts, "@"));
+  std::string new_email = base::StringToLowerASCII(JoinString(parts, at));
   VLOG(1) << "Canonicalized " << email_address << " to " << new_email;
   return new_email;
 }