Atomic ops: Sync with Chromium and add unit test.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/129813008

Patch from Cosmin Truta <ctruta@gmail.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19738 ce2b1a6d-e550-0410-aec6-3dcde31c8c00