Move raw pthreads usage to base primitives.

BUG=889703

Change-Id: I901c546c8329ea7082e11eaaae0bced60f376bf4
Reviewed-on: https://chromium-review.googlesource.com/1242763
Commit-Queue: Anand Mistry <amistry@chromium.org>
Reviewed-by: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594938}
4 files changed