Merge branch 'direct-calls' into buffer_pools_for_realsies

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

config.m4

doc/environment_variables.md

gRPC-Core.podspec

grpc.gemspec

package.xml

src/core/ext/client_config/subchannel.c

src/core/ext/transport/chttp2/transport/chttp2_plugin.c

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

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

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

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

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

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

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

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