Merge github.com:grpc/grpc into slice_with_exec_ctx

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

config.m4

doc/connection-backoff.md

gRPC-Core.podspec

grpc.gemspec

include/grpc++/impl/codegen/completion_queue.h

include/grpc++/impl/codegen/server_interface.h

package.xml

src/compiler/python_generator.cc

src/core/ext/client_channel/http_connect_handshaker.c

src/core/ext/client_channel/subchannel.c

src/core/ext/lb_policy/grpclb/grpclb.c

src/core/ext/resolver/dns/native/dns_resolver.c

src/core/ext/transport/chttp2/client/chttp2_connector.c

src/core/ext/transport/chttp2/client/chttp2_connector.h

...ore/ext/transport/chttp2/client/insecure/channel_create.c