code: func (c *BackgroundService) StartObserving(service string) (*gcdmessage.ChromeResponse, error) {
  	var v BackgroundServiceStartObservingParams
  	v.Service = service
  	return c.StartObservingWithParams(&v)
  }
docs: // StartObserving - Enables event updates for the service.
  // service -  enum values: backgroundFetch, backgroundSync