GitLab

This is a follow-up to https://chromium-review.googlesource.com/c/1305891

Missed that Mac had its own impl.
Example problematic trace because of this http://crash/18c6999290e01f89

Made all impls match waitable_event_win.cc
(also ignoring the ScopedEventWaitActivity when idle)

R=fdoray@chromium.org

Bug: 899897
Change-Id: Ib5aa1cec487f80a6f1d603658279666ee0d1de60
Reviewed-on: https://chromium-review.googlesource.com/c/1336073Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608511}