Port Chromium's atomicops to WebRTC

Porting Chromium's base/atomicops.h and friends into WebRTC.

Included the original unit test in Chromium.
Review URL: https://webrtc-codereview.appspot.com/964026

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@3241 4adac7df-926f-26a2-2b94-8c16560cd09d
10 files changed