Huh, I wonder what the crouton developer was talking about then. No encrypted disk? (I don't have Chrome OS, I was just guessing what the crouton README might mean.)
Further down in the Crouton Readme: "Note that developer mode, in its default configuration, is completely insecure, so don't expect a password in your chroot to keep anyone from your data. crouton does support encrypting chroots, but the encryption is only as strong as the quality of your passphrase."