Move files in util/ to common/.

The directory structure for Blink scheduler is changing. The new
convention deprecates util/ and the files in util/ should go to
common/ now. Headers used by non-scheduler code are moved to
public/.

Bug: 826203
Change-Id: I617deec92f3d34fc0bc82e3211bdd223e90339be
Reviewed-on: https://chromium-review.googlesource.com/c/1301578
Commit-Queue: Yuta Kitamura <yutak@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603471}
25 files changed