message: [XLA] When creating an HloInstruction from a proto, returns an error if the
  apply_to function is missing.
diff: @@ -599,6 +599,11 @@ StatusOr<std::unique_ptr<HloInstruction>> HloInstruction::CreateFromProto(
  instruction->AppendOperand(instruction_map.at(operand_id));
  }
  if (instruction->opcode() != HloOpcode::kFusion) {
  + if (instruction->opcode() == HloOpcode::kCall) {
  + TF_RET_CHECK(proto.called_computation_ids_size() == 1)
  + << "Call should have 1 called computation but has "
  + << proto.called_computation_ids_size();
  + }
  for (const int64 computation_id : proto.called_computation_ids()) {
  instruction->called_computations_.push_back(
  computation_map.at(computation_id));
  