Reland "Implement ES6 symbol registry and predefined symbols"

Only change relative to original CL is the updated assertion condition at objects-inl.h:2119

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/204913006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20136 ce2b1a6d-e550-0410-aec6-3dcde31c8c00