A hack / workaround for google/protobuf#1450, to get a stock version of Protocol Buffers 2.6.1 to work under UBSan. This is useful for (e.g.) building applications on Ubuntu 14.04 or 16.04, where you want to continue using the distro-provided protobuf library packaging instead of upgrading or patching the source.
There are two steps.
Replace every 16 in the generated .pb.cc files with this.  For example, if you use GNU Make to generate your .pb.cc files:
%.pb.cc %.pb.h %_pb2.py: %.proto