Merge pull request #4089 from yang-g/initial_string

BUILD

Makefile

binding.gyp

build.yaml

gRPC.podspec

src/core/client_config/connector.h

src/core/client_config/default_initial_connect_string.c

src/core/client_config/initial_connect_string.c

src/core/client_config/initial_connect_string.h

src/core/client_config/subchannel.c

src/core/iomgr/pollset_posix.c

src/core/iomgr/tcp_server.h

src/core/iomgr/tcp_server_posix.c

src/core/iomgr/tcp_server_windows.c

src/core/surface/channel_create.c

src/core/surface/secure_channel_create.c

src/core/transport/chttp2/hpack_encoder.c

test/core/client_config/lb_policies_test.c

test/core/client_config/set_initial_connect_string_test.c

test/core/end2end/tests/hpack_size.c