Before we used the hole value for this purpose, but this does not work once we
start using the hole value for other purposes in the optimizing compiler.

Review URL: http://codereview.chromium.org/6116001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6210 ce2b1a6d-e550-0410-aec6-3dcde31c8c00