new warning. needs to be fixed. 

From here: 

https://logs.chromium.org/v/?s=chromeos%2Fbb%2Fchromiumos.tryserver%2Fchromiumos-sdk%2F2722%2F%2B%2Frecipes%2Fsteps%2FInitSDK%2F0%2Fstdout


grpc-1.3.0-r1: x86_64-pc-linux-gnu-clang -pthread  -Ithird_party/googletest/googletest/include  -g -Wall -Wextra -Werror -Wno-long-long -Wno-unused-parameter -DOSATOMIC_USE_INLINED=1 -O2 -fPIC -I. -Iinclude -I/var/tmp/portage/dev-libs/grpc-1.3.0-r1/work/grpc-1.3.0/gens -DNDEBUG -DINSTALL_PREFIX=\"/usr\"     -DTSI_OPENSSL_ALPN_SUPPORT=0 -O2 -pipe -std=c99 -Wsign-conversion -Wconversion -Wshadow -Wextra-semi   -MMD -MF /var/tmp/portage/dev-libs/grpc-1.3.0-r1/work/grpc-1.3.0/objs/opt/src/core/lib/channel/handshaker_factory.dep -c -o /var/tmp/portage/dev-libs/grpc-1.3.0-r1/work/grpc-1.3.0/objs/opt/src/core/lib/channel/handshaker_factory.o src/core/lib/channel/handshaker_factory.c
grpc-1.3.0-r1: src/core/lib/channel/channel_args.c:228:23: error: implicit conversion changes
grpc-1.3.0-r1:       signedness: 'grpc_compression_algorithm' to 'int'
grpc-1.3.0-r1:       [-Werror,-Wsign-conversion]
grpc-1.3.0-r1:   tmp.value.integer = algorithm;
grpc-1.3.0-r1:                     ~ ^~~~~~~~~
grpc-1.3.0-r1: x86_64-pc-linux-gnu-clang -pthread  -Ithird_party/googletest/googletest/include  -g -Wall -Wextra -Werror -Wno-long-long -Wno-unused-parameter -DOSATOMIC_USE_INLINED=1 -O2 -fPIC -I. -Iinclude -I/var/tmp/portage/dev-libs/grpc-1.3.0-r1/work/grpc-1.3.0/gens -DNDEBUG -DINSTALL_PREFIX=\"/usr\"     -DTSI_OPENSSL_ALPN_SUPPORT=0 -O2 -pipe -std=c99 -Wsign-conversion -Wconversion -Wshadow -Wextra-semi   -MMD -MF /var/tmp/portage/dev-libs/grpc-1.3.0-r1/work/grpc-1.3.0/objs/opt/src/core/lib/channel/handshaker_registry.dep -c -o /var/tmp/portage/dev-libs/grpc-1.3.0-r1/work/grpc-1.3.0/objs/opt/src/core/lib/channel/handshaker_registry.o src/core/lib/channel/handshaker_registry.c
grpc-1.3.0-r1: 1 error generated.