Last attempt failed because of too agressive growing and no proper GC
scheduling.

Also refactor live object iteration on the way to avoid a branch when we
know that we will succeed.

Bug: chromium:651354
Change-Id: I8f52cbc79ac293989fb7c29c492d4ae4afe5ebe4
Reviewed-on: https://chromium-review.googlesource.com/544829
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46245}