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: default.go
    path of file: ./repos/corteza/server/vendor/golang.org/x/oauth2/google
    
    the code of the file until where you have to start completion: // Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package google

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"os"
	"path/filepath"
	"runtime"
	"sync"
	"time"

	"cloud.google.com/go/compute/metadata"
	"golang.org/x/oauth2"
	"golang.org/x/oauth
    
func (c *Credentials) GetUniverseDomain() (string, error) {
	c.udMu.Lock()
	defer c.udMu.Unlock()
	if c.universeDomain == "" && metadata.OnGCE() {
		// If we're on Google Compute Engine, an App Engine standard second
		// generation runtime, or App Engine flexible, use the metadata server.
		err := c.computeUniverseDomain()
		if err != nil {
			return "", err
		}
	}
	// If not on Google Compute Engine, or in case of any non-error path in
	// computeUniverseDomain that did not set universeDomain, set the default
	// universe domain.
	if c.universeDomain == "" {
		c.universeDomain = universeDomainDefault
	}
	return c.universeDomain, nil
}