Replace CopyMap(constructor->initial_map()) by Map::Create(constructor)

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/218633014

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20437 ce2b1a6d-e550-0410-aec6-3dcde31c8c00