Fix GCMole warning

R=adamk@chromium.org
TBR=mstarzinger@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/73123002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17763 ce2b1a6d-e550-0410-aec6-3dcde31c8c00