Check in a pristine copy of rtc::Event into Chromium.

This is the first of three steps towards making WebRTC use Chromium's WaitableEvent implementation.

The eventual benefits of this are to make WebRTCs TaskQueue
implementation get the benefits of WaitableEvent (e.g. not waiting on an event
inside a task that runs on a queue whose traits don't allow that)
and not violate Chromium's task queue traits once we have more thread
sharing going on.

Bug: 689520
Change-Id: I970f804fc16aa46fa9c4bc6f1abd857b7129222e
Reviewed-on: https://chromium-review.googlesource.com/789871
Reviewed-by: Henrik Grunell <grunell@chromium.org>
Commit-Queue: Tommi <tommi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519263}
2 files changed