The dependency between restoring iterability and the Scavenger is
explicit. Delayed chunks are thus not needed anymore.

Bug: chromium:791043
Change-Id: I9f2c95c1856f53299af2737f922a3cb4cc578aa5
Reviewed-on: https://chromium-review.googlesource.com/805816Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49855}