message: Add a num_threads field to InterpreterCreationResources, to allow using InterpreterBuilder::SetNumThreads rather than Interpreter::SetNumThreads,
  since we want to minimize the use of mutating methods on Interpreter.
diff: @@ -41,11 +41,21 @@ struct InterpreterCreationResources {
  // and maintains it through out the lifetime of `TfLiteInterpreterWrapper`.
  TfLiteDelegate* optional_delegate;
  + // Number of threads to use, or -1 to use the default number of threads.
  + int num_threads = -1;
  +
  // Apply the InterpreterCreationResources to the InterpreterBuilder.
  + // Note: caller is responsible for ensuring that arguments are valid,
  + // e.g. that num_threads >= -1.
  void ApplyTo(tflite::InterpreterBuilder* interpreter_builder) const {
  if (optional_delegate != nullptr) {
  interpreter_builder->AddDelegate(optional_delegate);
  }
  + if (num_threads != -1) {
  + // We ignore the TfLiteStatus return value here; caller is responsible
  + // for checking that num_threads is valid.
  + (void)interpreter_builder->SetNumThreads(num_threads);
  + }
  }
  };
  