code: func registerAPIMetrics(attributes ...string) *apiCallMetrics {
  	metrics := &apiCallMetrics{
  		latency: prometheus.NewHistogramVec(
  			prometheus.HistogramOpts{
  				Name: "cloudprovider_gce_api_request_duration_seconds",
  				Help: "Latency of a GCE API call",
  			},
  			attributes,
  		),
  		errors: prometheus.NewCounterVec(
  			prometheus.CounterOpts{
  				Name: "cloudprovider_gce_api_request_errors",
  				Help: "Number of errors for an API call",
  			},
  			attributes,
  		),
  	}
  
  	prometheus.MustRegister(metrics.latency)
  	prometheus.MustRegister(metrics.errors)
  
  	return metrics
  }
docs: // registerApiMetrics adds metrics definitions for a category of API calls.