Build fix for CustomProtocolManagerMac after r141658.

Patch by Benjamin Poulain <bpoulain@apple.com> on 2013-02-01

* Shared/Network/CustomProtocols/mac/CustomProtocolManagerMac.mm:
(WebKit::CustomProtocolManager::supplementName): I accidentally typed "const" twice twice.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141663 268f45cc-cd09-0410-ab3c-d52691b4dbfc