message: TFL TOCO: make buffers_to_write carrying offsets instead of TOCO Array.
  so that later we can attach other types of data into the buffer, such as metadata.
diff: @@ -207,7 +207,8 @@ void LoadOperatorsMap(
  Offset<Vector<Offset<Tensor>>> ExportTensors(
  const Model& model, const details::TensorsMap& tensors_map,
  - FlatBufferBuilder* builder, std::vector<const Array*>* buffers_to_write,
  + FlatBufferBuilder* builder,
  + std::vector<Offset<Vector<uint8_t>>>* buffers_to_write,
  const std::set<int32_t>& variable_tensor_indices) {
  // In the end we will need to produce a vector sorted by the indices of the
  // tensors in the tensors_map.
  @@ -219,7 +220,7 @@ Offset<Vector<Offset<Tensor>>> ExportTensors(
  int buffer_index = buffers_to_write->size();
  auto type = DataType::Serialize(array.data_type);
  - buffers_to_write->push_back(&array);
  + buffers_to_write->push_back(DataBuffer::Serialize(array, builder));
  std::vector<int> shape;
  if (array.has_shape()) {
  @@ -413,13 +414,13 @@ Offset<Vector<Offset<Operator>>> ExportOperators(
  }
  Offset<Vector<Offset<Buffer>>> ExportBuffers(
  - const Model& model, const std::vector<const Array*>& buffers_to_write,
  + const Model& model,
  + const std::vector<Offset<Vector<uint8_t>>>& buffers_to_write,
  FlatBufferBuilder* builder) {
  std::vector<Offset<Buffer>> buffer_vector;
  - for (const Array* array_ptr : buffers_to_write) {
  - const Array& array = *array_ptr;
  - Offset<Vector<uint8_t>> data_buffer = DataBuffer::Serialize(array, builder);
  - buffer_vector.push_back(CreateBuffer(*builder, data_buffer));
  + buffer_vector.reserve(buffers_to_write.size());
  + for (const auto buffer : buffers_to_write) {
  + buffer_vector.push_back(CreateBuffer(*builder, buffer));
  }
  return builder->CreateVector(buffer_vector);
  }
  @@ -475,9 +476,9 @@ tensorflow::Status Export(
  details::LoadOperatorsMap(model, &operators_map, ops_by_type,
  params.enable_select_tf_ops);
  - std::vector<const Array*> buffers_to_write;
  - Array empty_array;
  - buffers_to_write.push_back(&empty_array);
  + std::vector<Offset<Vector<uint8_t>>> buffers_to_write;
  + // Insert an empty buffer to the beginning of the list.
  + buffers_to_write.push_back(0);
  auto op_codes =
  ExportOperatorCodes(model, ops_by_type, operators_map, &builder, params);
  