The iterator already provides the size.

Bug: chromium:651354
Change-Id: I683bfe5c82441bf39c21b18daa58eba91b798c64
Reviewed-on: https://chromium-review.googlesource.com/543495
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46092}