Make -Wshadow happy.

LOG=y
BUG=v8:3073
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/119983003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18463 ce2b1a6d-e550-0410-aec6-3dcde31c8c00