A MessageObject is a purely internal object to hold information about

A MessageObject is a purely internal object to hold information about
an error message that needs to be generated and reported. This change
hides all of the error information from JavaScript code so user
callbacks cannot get hold of it.

Review URL: http://codereview.chromium.org/6368051

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6574 ce2b1a6d-e550-0410-aec6-3dcde31c8c00