Adds a test case demonstrating that when HPACK compression is disabled and incremental encoding is used, spdy::HpackEncoder emits \0-delimited values on the wire. HPACK compression is always enabled in production. http://cs/search/?q=gfe2_http2_compress_headers_to gfe-relnote: n/a (test only) PiperOrigin-RevId: 284839022 Change-Id: Ifdd79eb2008b239b685732d9e999ea981a0aeef2