Merge remote-tracking branch 'upstream/master' into handshaker_api

BUILD

CMakeLists.txt

Makefile

build.yaml

doc/health-checking.md

examples/php/route_guide/README.md

include/grpc/grpc.h

src/core/ext/lb_policy/grpclb/grpclb.c

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

src/core/lib/channel/channel_stack.h

src/core/lib/channel/channel_stack_builder.h

src/core/lib/channel/context.h

src/core/lib/iomgr/tcp_server_posix.c

src/core/lib/security/context/security_context.h

src/core/lib/surface/channel.h

src/core/lib/surface/channel_init.h

src/core/lib/surface/server.c

src/core/lib/transport/byte_stream.h

src/core/lib/transport/metadata.h

src/core/lib/transport/metadata_batch.c