Don't URL-encode slashes in gRPC request headers. (#6310)

Per internal document go/api-url-encoding (approved on 2017-04-20), "the
client library will %-encode everything except "/" and unreserved
characters, and the server will %-decode everything except "%2F"
and %2f"

This is currently affecting a private API which passes a resource name
(containing slashes) as a query parameter over gRPC.
2 files changed