Make namespace more explicit.

test/cpp/util/byte_buffer_proto_helper.h

@@ -27,12 +27,13 @@
 namespace grpc {
 namespace testing {
 
-bool ParseFromByteBuffer(ByteBuffer* buffer, grpc::protobuf::Message* message);
+bool ParseFromByteBuffer(ByteBuffer* buffer,
+                         ::grpc::protobuf::Message* message);
 
 std::unique_ptr<ByteBuffer> SerializeToByteBuffer(
-    grpc::protobuf::Message* message);
+    ::grpc::protobuf::Message* message);
 
-bool SerializeToByteBufferInPlace(grpc::protobuf::Message* message,
+bool SerializeToByteBufferInPlace(::grpc::protobuf::Message* message,
                                   ByteBuffer* buffer);
 
 }  // namespace testing