message: Reflecting changes from cl/262235093, replacing DatasetBase::IsStateful() with error raising DatasetBase::CheckExternalState().
diff: @@ -233,7 +233,7 @@ class SequenceFileDatasetOp : public DatasetOpKernel {
  return "SequenceFileDatasetOp::Dataset";
  }
  - bool IsStateful() const override { return false; }
  + Status CheckExternalState() const override { return Status::OK(); }
  protected:
  Status AsGraphDefInternal(SerializationContext* ctx,
  