Handle exception when retrieving toJSON function in JSON.stringify.

R=mvstanton@chromium.org
BUG=349335
LOG=N

Review URL: https://codereview.chromium.org/187603002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19670 ce2b1a6d-e550-0410-aec6-3dcde31c8c00