You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: namespace.go
    path of file: ./repos/sealer/vendor/github.com/docker/go-metrics
    
    the code of the file until where you have to start completion: package metrics

import (
	"fmt"
	"sync"

	"github.com/prometheus/client_golang/prometheus"
)

type Labels map[string]string

// NewNamespace returns a namespaces that is responsible for managing a collection of
// metrics for a particual namespace and subsystem
//
// labels allows const labels to be added to all metrics created in this namespace
// and are commonly used for data like application version and git commit
func NewNamespace(name, subsystem strin
    
func (n *Namespace) NewRequestTotalMetric(handlerName string) *HTTPMetric {
	labels := prometheus.Labels(n.labels)
	labels["handler"] = handlerName
	metric := prometheus.NewCounterVec(
		prometheus.CounterOpts{
			Namespace:   n.name,
			Subsystem:   n.subsystem,
			Name:        "requests_total",
			Help:        "Total number of HTTP requests made.",
			ConstLabels: prometheus.Labels(labels),
		},
		[]string{"code", "method"},
	)
	httpMetric := &HTTPMetric{
		Collector:   metric,
		handlerType: InstrumentHandlerCounter,
	}
	n.Add(httpMetric)
	return httpMetric
}