... so that it is no longer needed to iterate over other lists.
This CL also moves data handler maps to the RO roots list (because they are RO).

Bug: v8:8015
Change-Id: If21fe5bac5a6ac1e44a47783ad930df5fcecda9a
Reviewed-on: https://chromium-review.googlesource.com/1240134Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56169}