Previously, we would accept gzip-encoded responses, but only because we
were letting requests decode *all* responses (even object data). This
restores the previous capability, but with tighter controls about which
requests will accept gzipped responses and where the decoding happens.
Change-Id: I4fd8b97207b9ab01b1bcf825cc16efd8ad46344a
Related-Bug: 1282861
Related-Bug: 1338464