Load the actor class.

        Args:
            driver_id: Driver ID of the actor.
            function_descriptor: Function descriptor of the actor constructor.

        Returns:
            The actor class.

def load_actor_class(self, driver_id, function_descriptor):
        """Load the actor class.

        Args:
            driver_id: Driver ID of the actor.
            function_descriptor: Function descriptor of the actor constructor.

        Returns:
            The actor class.
        """
        function_id = function_descriptor.function_id
        # Check if the actor class already exists in the cache.
        actor_class = self._loaded_actor_classes.get(function_id, None)
        if actor_class is None:
            # Load actor class.
            if self._worker.load_code_from_local:
                driver_id = ray.DriverID.nil()
                # Load actor class from local code.
                actor_class = self._load_actor_from_local(
                    driver_id, function_descriptor)
            else:
                # Load actor class from GCS.
                actor_class = self._load_actor_class_from_gcs(
                    driver_id, function_descriptor)
            # Save the loaded actor class in cache.
            self._loaded_actor_classes[function_id] = actor_class

            # Generate execution info for the methods of this actor class.
            module_name = function_descriptor.module_name
            actor_class_name = function_descriptor.class_name
            actor_methods = inspect.getmembers(
                actor_class, predicate=is_function_or_method)
            for actor_method_name, actor_method in actor_methods:
                method_descriptor = FunctionDescriptor(
                    module_name, actor_method_name, actor_class_name)
                method_id = method_descriptor.function_id
                executor = self._make_actor_method_executor(
                    actor_method_name,
                    actor_method,
                    actor_imported=True,
                )
                self._function_execution_info[driver_id][method_id] = (
                    FunctionExecutionInfo(
                        function=executor,
                        function_name=actor_method_name,
                        max_calls=0,
                    ))
                self._num_task_executions[driver_id][method_id] = 0
            self._num_task_executions[driver_id][function_id] = 0
        return actor_class