Harden Runtime_FunctionSetPrototype, Isolate::PrintStack

BUG=chromium:377209
LOG=n
R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/306543002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21584 ce2b1a6d-e550-0410-aec6-3dcde31c8c00