88153 - keep javascript URLs in Page Info dialog from running with system principal
by making the iframe's source about:blank initially and sandboxing it
with type=content. sr=blake, r=mstoltz.
88417 - Disallow setting of location.host and other location subparts cross-domain
r=mstoltz, sr=jst.
git-svn-id: svn://10.0.0.236/trunk@99008 18797224-902f-48f8-a5cc-f745e15eee43