Summary:
Reuses the original property descriptor when overwriting / polyfilling globals to ensure enumerability and writability are the same
Closes https://github.com/facebook/react-native/pull/7704
Differential Revision: D3338119
Pulled By: davidaurelio
fbshipit-source-id: ab456324a3346cd3ec8b2c3e3a2378408c92087c