created during bootstrapping. Without this change we 
risk having weird flags set on the map for the null
value (among others), which can lead to crashes.
Review URL: http://codereview.chromium.org/552195

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3725 ce2b1a6d-e550-0410-aec6-3dcde31c8c00