message: Update hlo constant folding to use returned error status
diff: @@ -183,9 +183,10 @@ Status ConstantFolderVisitor::HandleConvert(HloInstruction* convert,
  HloInstruction* operand) {
  if (operand->opcode() == HloOpcode::kConstant) {
  const Literal& src_literal = operand->literal();
  - std::unique_ptr<Literal> new_constant =
  + std::unique_ptr<Literal> new_constant;
  + TF_ASSIGN_OR_RETURN(new_constant,
  LiteralUtil::ConvertIfSrcTypeMatches(src_literal,
  - convert->shape().element_type());
  + convert->shape().element_type()));
  return ReplaceWithConstant(convert, std::move(new_constant));
  }
  return Status::OK();
  