new persistent semantics

adds copying and autodispose as traits

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

BUG=

Review URL: https://codereview.chromium.org/23401003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16588 ce2b1a6d-e550-0410-aec6-3dcde31c8c00