This visitor can be reused by the full MC when seeding root items.

Bug: chromium:750084
Change-Id: I9d46ce55737961d8f72a34b06f3314c8f75f3b4d
Reviewed-on: https://chromium-review.googlesource.com/591451Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46972}