than 64 distinct InstanceTypes. We are hitting that boundary, so this
check needs to be more comprehensive. In fact, two bits need to be
tested: verify that kNotStringTag isn't set, and that kInternalizedTag
is set.

BUG=
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/17895002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15358 ce2b1a6d-e550-0410-aec6-3dcde31c8c00