It avoids strange performance behavior where hot functions do not
get optimized if there is no GC to promote them, and it does not seem
to hurt us otherwise.

Review URL: http://codereview.chromium.org/6594073

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7016 ce2b1a6d-e550-0410-aec6-3dcde31c8c00