optimize show()
optimize show()

Summary: Implement two show() functions with std::string.

Reviewed By: NTillmann

Differential Revision: D16618062

fbshipit-source-id: d2e2036986a3b73a7fff1e727ac246e92c54f30d

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex