code: def _serve_plugins_listing(self, request):
      
      response = {}
      for plugin in self._plugins:
        start = time.time()
        response[plugin.plugin_name] = plugin.is_active()
        elapsed = time.time() - start
        logger.info(
            'Plugin listing: is_active() for %s took %0.3f seconds',
            plugin.plugin_name, elapsed)
      return http_util.Respond(request, response, 'application/json')
docs: Serves an object mapping plugin name to whether it is enabled.
  
      Args:
        request: The werkzeug.Request object.
  
      Returns:
        A werkzeug.Response object.