Resolved merge conflicts with upstream/release-0_12

BUILD

Makefile

binding.gyp

build.yaml

gRPC.podspec

grpc.gemspec

include/grpc/grpc.h

package.json

src/core/surface/call.c

src/core/surface/validate_metadata.c

src/core/transport/chttp2/bin_encoder.c

src/core/transport/chttp2/bin_encoder.h

src/core/transport/chttp2/hpack_encoder.c

src/core/transport/chttp2/hpack_parser.c

src/core/transport/metadata.c

src/core/transport/metadata.h

src/node/ext/call.cc

src/node/ext/node_grpc.cc

src/node/interop/async_delay_queue.js

src/node/src/metadata.js