GitLab

Added AsyncDispatcher class which implements async dispatcher interface
for Fuchsia. It will be used in MessagePumpFuchsia. This will allow to
run FIDL on Chromium threads.

The implementation is based largely on the default async loop. That code
has been translated to C++ with all features that we don't need in
chromium removed.

Bug: 831384
Change-Id: I76459d364e1a4864dbe6f76f582b9fb87c79e027
Reviewed-on: https://chromium-review.googlesource.com/1003073
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550416}