It turns out that having PC pointing _exactly_ at callback entry
point is quite probable.

BUG=crbug/60753

Review URL: http://codereview.chromium.org/4169005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5721 ce2b1a6d-e550-0410-aec6-3dcde31c8c00