Merge github.com:grpc/grpc into secsvr

Makefile

build.yaml

include/grpc++/impl/rpc_service_method.h

src/core/iomgr/tcp_windows.c

src/core/security/credentials.h

src/core/security/credentials_posix.c

src/core/security/credentials_win32.c

src/core/security/google_default_credentials.c

src/core/security/json_token.c

src/core/support/string.c

src/core/support/string.h

src/core/transport/chttp2/timeout_encoding.c

src/core/transport/connectivity_state.c

src/core/transport/connectivity_state.h

src/cpp/proto/proto_utils.cc

templates/Makefile.template

test/core/security/credentials_test.c

test/core/support/string_test.c

test/core/transport/connectivity_state_test.c

tools/run_tests/jobset.py