Reland r19897 "Fix memory leak caused by treating Code::next_code_link as strong in marker.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/212553003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20282 ce2b1a6d-e550-0410-aec6-3dcde31c8c00