the megamorphic load case in hydrogen. A simple approach is to
wrap the probe activity in a hydrogen instruction.

The instruction is novel in that it always tail-calls away.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/535873002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23772 ce2b1a6d-e550-0410-aec6-3dcde31c8c00