During concurrent marking we need special handling of object layout
changes that remove tagged in-object fields or replaces them with
untagged in-object fields.

This patch adds a function for notifying object layout changes and
verification code that is triggered on each map change in runtime.

BUG=chromium:694255

Review-Url: https://codereview.chromium.org/2702303002
Cr-Commit-Position: refs/heads/master@{#43342}