Promise should not be enumerable in the global object.

BUG=352597
R=rossberg@chromium.org
LOG=Y

Review URL: https://codereview.chromium.org/211943004

Patch from Yutaka Hirano <yhirano@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20268 ce2b1a6d-e550-0410-aec6-3dcde31c8c00