Inline pointers visitation instead of handling recursive marking.

Bug: chromium:738831
Change-Id: I0840258988c3097119f6299f0e1b6759b55fbd27
Reviewed-on: https://chromium-review.googlesource.com/559346
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46414}