Summary:
Base64 encoding can easily cause OOMs for large payloads.
In the long-term, it would be great to have a way of streaming these
responses so we don't allocate 50MB chunks of memory at once.
Reviewed By: jknoxville
Differential Revision: D17951353
fbshipit-source-id: a5d7b8242892518590ac95c1d9751f24d20dc40e
182b4e1b1f