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

grpc.def

include/grpc/impl/codegen/sync.h

src/core/iomgr/iomgr.c

src/core/iomgr/iomgr_internal.h

src/core/support/sync.c

src/core/transport/chttp2/internal.h

src/core/transport/chttp2/parsing.c

src/core/transport/chttp2/stream_lists.c

src/core/transport/chttp2/writing.c

src/core/transport/chttp2_transport.c

src/core/transport/metadata.c

src/core/transport/transport.c

src/python/grpcio/README.rst

...thon/grpcio/grpc/_cython/_cygrpc/completion_queue.pxd.pxi

...thon/grpcio/grpc/_cython/_cygrpc/completion_queue.pyx.pxi

src/python/grpcio/grpc/_cython/_cygrpc/grpc.pxi

src/python/grpcio/grpc/_cython/imports.generated.c

src/python/grpcio/grpc/_cython/imports.generated.h

src/python/grpcio/tests/_runner.py

src/python/grpcio/tests/tests.json