Merge branch 'slice_with_exec_ctx' into eliminate_mdstr

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

config.m4

gRPC-Core.podspec

grpc.gemspec

include/grpc++/channel.h

include/grpc++/support/channel_arguments.h

include/grpc/impl/codegen/grpc_types.h

package.xml

src/core/ext/client_channel/client_channel.c

src/core/ext/client_channel/lb_policy_registry.c

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

src/core/ext/load_reporting/load_reporting_filter.c

src/core/ext/transport/chttp2/transport/chttp2_transport.c

src/core/ext/transport/chttp2/transport/hpack_encoder.c

src/core/ext/transport/chttp2/transport/hpack_parser.c

src/core/ext/transport/chttp2/transport/hpack_table.c