Use TimeDelta::operator/() more, misc. edition.

Bug: 1104532
Change-Id: Icc7244ef277171fbc37f1fc3ca89837a629aa01b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2354628


Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Mike Pinkerton <pinkerton@chromium.org>
Reviewed-by: Mike Pinkerton <pinkerton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798124}