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Per the note, you probably don't need to use TickClock or
DefaultTickClock anymore. Stick that note in both TickClock and
DefaultTickClockheaders instead of just DefaultTickClock.

Bug: None
Test: None
Change-Id: I7cdaa5b198ad06b230e2b0406c51f49f769b0794
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2547749
Commit-Queue: David Munro <davidmunro@google.com>
Auto-Submit: David Munro <davidmunro@google.com>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830072}