Merge github.com:grpc/grpc into metadata_filter

src/core/ext/client_channel/http_connect_handshaker.c

src/core/ext/client_channel/http_connect_handshaker.h

src/python/grpcio_tests/tests/qps/benchmark_client.py

src/python/grpcio_tests/tests/stress/client.py

templates/tools/doxygen/Doxyfile.include

test/http2_test/http2_base_server.py

test/http2_test/http2_test_server.py

tools/doxygen/Doxyfile.c++

tools/doxygen/Doxyfile.c++.internal

tools/doxygen/Doxyfile.core

tools/doxygen/Doxyfile.core.internal