Add support for movable only functors with void return type. Non void
return type is already supported.
Bug: webrtc:10138
Change-Id: If2ae2b5ab7244a0e932bceff7d9853c030805688
Reviewed-on: https://webrtc-review.googlesource.com/c/116740
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26186}