Grab prefixes after a :class:`~google.cloud.iterator.Page` started.

    :type iterator: :class:`~google.api_core.page_iterator.Iterator`
    :param iterator: The iterator that is currently in use.

    :type page: :class:`~google.cloud.api.core.page_iterator.Page`
    :param page: The page that was just created.

    :type response: dict
    :param response: The JSON API response for a page of blobs.

def _blobs_page_start(iterator, page, response):
    """Grab prefixes after a :class:`~google.cloud.iterator.Page` started.

    :type iterator: :class:`~google.api_core.page_iterator.Iterator`
    :param iterator: The iterator that is currently in use.

    :type page: :class:`~google.cloud.api.core.page_iterator.Page`
    :param page: The page that was just created.

    :type response: dict
    :param response: The JSON API response for a page of blobs.
    """
    page.prefixes = tuple(response.get("prefixes", ()))
    iterator.prefixes.update(page.prefixes)