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

.gitmodules

BUILD

Makefile

build.json

gRPC.podspec

src/core/census/grpc_filter.c

src/core/census/grpc_filter.h

src/core/iomgr/tcp_windows.c

src/core/surface/channel_create.c

src/core/surface/secure_channel_create.c

src/core/surface/server.c

templates/Makefile.template

third_party/googletest

tools/doxygen/Doxyfile.core.internal

tools/run_tests/jobset.py

tools/run_tests/run_sanity.sh

tools/run_tests/sources_and_headers.json

vsprojects/grpc/grpc.vcxproj

vsprojects/grpc/grpc.vcxproj.filters

vsprojects/grpc_unsecure/grpc_unsecure.vcxproj