Replace calls to IsDark() where possible.

For example, PickContrastingColor() is a better way of picking between a light
and dark color to place against a background, because it guarantees using the
one that actually contrasts more.

Bug: 659451
Change-Id: I27febca506971ad7ce6db265fc92d680c3f81575
Reviewed-on: https://chromium-review.googlesource.com/c/1404406
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621691}
3 files changed