message: Add Unimplemented visitor for token element types to HLO evaluator.
  The evaluator would crash when encountering an instruction which produced a
  TOKEN shape.
diff: @@ -190,6 +190,11 @@ HloEvaluator::HloEvaluator(int64 max_loop_iterations)
  return Unimplemented(
  "HloEvaluatorTypedVisitor: unhandled primitive type: OPAQUE.");
  });
  + typed_visitors_[TOKEN] =
  + absl::make_unique<FunctionVisitor>([](HloInstruction*) {
  + return Unimplemented(
  + "HloEvaluatorTypedVisitor: unhandled primitive type: TOKEN.");
  + });
  }
  template <typename LiteralPtr>
  