Use base::TimeDelta::is_zero() where appropriate.

Instead of constructing another TimeDelta to compare to.
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1908623003

Cr-Commit-Position: refs/heads/master@{#389311}
53 files changed