Merge pull request #11499 from markdroth/trailers_only

src/core/ext/transport/chttp2/transport/chttp2_transport.c

src/core/ext/transport/chttp2/transport/frame_rst_stream.c

src/core/ext/transport/chttp2/transport/hpack_encoder.c

src/core/ext/transport/chttp2/transport/hpack_encoder.h

src/core/ext/transport/chttp2/transport/internal.h

src/core/ext/transport/chttp2/transport/parsing.c

src/core/ext/transport/chttp2/transport/writing.c

src/core/lib/surface/call.c

src/core/lib/transport/transport.h

test/core/transport/chttp2/hpack_encoder_test.c

test/cpp/microbenchmarks/bm_chttp2_hpack.cc