code: func throttleImagePulling(imageService kubecontainer.ImageService, qps float32, burst int) kubecontainer.ImageService {
  	if qps == 0.0 {
  		return imageService
  	}
  	return &throttledImageService{
  		ImageService: imageService,
  		limiter:      flowcontrol.NewTokenBucketRateLimiter(qps, burst),
  	}
  }
docs: // throttleImagePulling wraps kubecontainer.ImageService to throttle image
  // pulling based on the given QPS and burst limits. If QPS is zero, defaults
  // to no throttling.