The refactoring also requires serialization of Map::prototype.

Bug: v8:7790
Change-Id: I240254d0a1f1beaf03b13d20cc7cc02c96f08069
Reviewed-on: https://chromium-review.googlesource.com/1219328
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55853}