Merge branch 'master' into svc_cfg2

BUILD

BUILD.gn

CMakeLists.txt

CONTRIBUTING.md

Makefile

build.yaml

config.m4

config.w32

gRPC-C++.podspec

gRPC-Core.podspec

grpc.gemspec

grpc.gyp

include/grpc/impl/codegen/grpc_types.h

package.xml

src/core/ext/filters/client_channel/client_channel.cc

.../ext/filters/client_channel/health/health_check_client.cc

...e/ext/filters/client_channel/health/health_check_client.h

src/core/ext/filters/client_channel/subchannel.cc

src/core/ext/filters/client_channel/subchannel.h

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