Given a tag, return the associated session.run() metadata.

    Args:
      tag: A string tag associated with the event.

    Raises:
      ValueError: If the tag is not found.

    Returns:
      The metadata in form of `RunMetadata` proto.

def RunMetadata(self, tag):
    """Given a tag, return the associated session.run() metadata.

    Args:
      tag: A string tag associated with the event.

    Raises:
      ValueError: If the tag is not found.

    Returns:
      The metadata in form of `RunMetadata` proto.
    """
    if tag not in self._tagged_metadata:
      raise ValueError('There is no run metadata with this tag name')

    run_metadata = config_pb2.RunMetadata()
    run_metadata.ParseFromString(self._tagged_metadata[tag])
    return run_metadata