Return MaybeHandle from NewRaw???String.

R=ishell@chromium.org

Review URL: https://codereview.chromium.org/223573002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20479 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Reland "Return MaybeHandle from NewConsString."

R=ishell@chromium.org

Review URL: https://codereview.chromium.org/223813002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20480 ce2b1a6d-e550-0410-aec6-3dcde31c8c00