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

.gitignore

BUILD

Makefile

build.json

gRPC.podspec

include/grpc/grpc.h

include/grpc/support/atm_gcc_atomic.h

include/grpc/support/atm_gcc_sync.h

include/grpc/support/atm_win32.h

src/core/channel/http_client_filter.c

src/core/channel/http_server_filter.c

src/core/client_config/resolvers/dns_resolver.c

...nt_config/subchannel_factory_decorators/add_channel_arg.c

...nt_config/subchannel_factory_decorators/add_channel_arg.h

...config/subchannel_factory_decorators/merge_channel_args.c

...config/subchannel_factory_decorators/merge_channel_args.h

src/core/iomgr/fd_posix.c

src/core/iomgr/fd_posix.h

src/core/iomgr/tcp_server_posix.c

src/core/support/stack_lockfree.c