class_docstr: Base class for a TFDS function decorator.
  
  When a decorated function is called, the method with the same name as this
  class is called on the registered loggers.
docstr: Initializes call metadata.
docstr_tok: ["Initializes","call","metadata","."]
code: def _start_call(self) -> call_metadata.CallMetadata:
      """Initializes call metadata."""
      return call_metadata.CallMetadata()
  
imports: import abc
  import atexit
  import collections
  import functools
  import threading
  from typing import Any, Callable, Dict, List, Optional, Tuple, TypeVar
  from absl import flags
  from tensorflow_datasets.core.logging import base_logger
  from tensorflow_datasets.core.logging import call_metadata
  from tensorflow_datasets.core.logging import logging_logger
  import wrapt
label_desc: Use image node_id 1 for calling the _FunctionDecorator obj's underlying member method code with example usage: obj._start_call() and returns: call_metadata