Check that after a weak callback, the handle is either dead or strong

BUG=346061
R=dcarney@chromium.org
LOG=y

Review URL: https://codereview.chromium.org/177943002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19534 ce2b1a6d-e550-0410-aec6-3dcde31c8c00