This turns the deoptimization entries from free-floating memory chunks
that were not considered part of the heap into true {Code} objects. By
marking them as immovable we get the same guarantees without the need
for side-stepping heap API methods.

R=jarin@chromium.org
BUG=v8:6792

Change-Id: I88e1795e52fb586f7ca960d08cd6d9d082f4df9b
Reviewed-on: https://chromium-review.googlesource.com/756851Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49257}