This CL ensures that elements kind transitions don't cause silent
mutable-to-constant field migrations when the following options
are enabled: --track_constant_fields --modify_map_inplace.

Bug: v8:5495, v8:6980
Change-Id: Ie28daab84f91d424110e71504b025a2e465bfe16
Reviewed-on: https://chromium-review.googlesource.com/753087
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49133}