Fix for a GCMole issue introduced in r21117.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/269743002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21121 ce2b1a6d-e550-0410-aec6-3dcde31c8c00