and use it in various places. Create null principals if asked for a codebase
principal for a codebase that doesn't have an inherent security context (eg
data: or javascript:). Bug 334407, r=biesi,dveditz, sr=darin
git-svn-id: svn://10.0.0.236/trunk@195823 18797224-902f-48f8-a5cc-f745e15eee43