message: [BufferAssignment] Sort allocation's "Assigned" objects before converting to a proto.
  This makes the buffer assignment's proto dump deterministic.
  RELNOTES: BufferAssignment's protocol buffer dump is now deterministic.
diff: @@ -101,6 +101,11 @@ BufferAllocationProto BufferAllocation::ToProto() const {
  proto_assigned->set_offset(buffer_offset_size.second.offset);
  proto_assigned->set_size(buffer_offset_size.second.size);
  }
  + std::sort(proto.mutable_assigned()->begin(), proto.mutable_assigned()->end(),
  + [](const BufferAllocationProto::Assigned& assign1,
  + const BufferAllocationProto::Assigned& assign2) {
  + return assign1.logical_buffer_id() < assign2.logical_buffer_id();
  + });
  return proto;
  }
  