This facility should be used in methods that run on known threads
(e.g. signaling, worker) and do not have blocking thread syncronization
operations via the Thread class such as Invoke, Sleep, etc.
This is a reland of an already reviewed cl (r6679) that got reverted by mistake.
TBR=xians@google.com,tommi@webrtc.org
Review URL: https://webrtc-codereview.appspot.com/21889004
git-svn-id: http://webrtc.googlecode.com/svn/trunk@6682 4adac7df-926f-26a2-2b94-8c16560cd09d