Do not try to serialize them into JSON to avoid crashing / hanging DevTools.

R=sgjesse@chromium.org
BUG=v8:1658,89268
TEST=none

Review URL: http://codereview.chromium.org/7832003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9123 ce2b1a6d-e550-0410-aec6-3dcde31c8c00