Otherwise fast path of scavenger gets a bit too complicated and heavy.

R=mstarzinger@chromium.org

Review URL: http://codereview.chromium.org/8217002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9561 ce2b1a6d-e550-0410-aec6-3dcde31c8c00