Make a Persistent ctor take const Persistent& instead of Persistent&.

BUG=
R=mstarzinger@chromium.org, svenpanne@chromium.org

Review URL: https://codereview.chromium.org/17580010

Patch from Marja Hölttä <marja@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15278 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Update the TSan-specific atomics implementation to match the current API.

BUG=128314

Review URL: https://codereview.chromium.org/17591005

Patch from Alexander Potapenko <glider@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15279 ce2b1a6d-e550-0410-aec6-3dcde31c8c00