Merge branch 'cp' into rollfwd

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

config.m4

gRPC-Core.podspec

grpc.gemspec

package.xml

src/core/ext/client_channel/client_channel.c

src/core/ext/client_channel/client_channel_plugin.c

src/core/ext/client_channel/http_connect_handshaker.c

src/core/ext/client_channel/http_connect_handshaker.h

src/core/ext/client_channel/http_proxy.c

src/core/ext/client_channel/http_proxy.h

src/core/ext/client_channel/proxy_mapper.c

src/core/ext/client_channel/proxy_mapper.h

src/core/ext/client_channel/proxy_mapper_registry.c

src/core/ext/client_channel/proxy_mapper_registry.h

src/core/ext/client_channel/subchannel.c