Document:
- Visitor

Bug: chromium:1056170
Change-Id: Icc0037befa73f043fcbf14ff4ff89be8b8940ee4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2235696Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68233}