How to use the @google-cloud/common.util.getUserAgentFromPackageJson function in @google-cloud/common

this.grpcMetadata.add('x-goog-api-client', [
    'gl-node/' + process.versions.node,
    'gccl/' + config.packageJson.version,
    'grpc/' + require('grpc/package.json').version
  ].join(' '));

  if (config.grpcMetadata) {
    for (var prop in config.grpcMetadata) {
      if (config.grpcMetadata.hasOwnProperty(prop)) {
        this.grpcMetadata.add(prop, config.grpcMetadata[prop]);
      }
    }
  }

  this.maxRetries = options.maxRetries;
  this.userAgent = util.getUserAgentFromPackageJson(config.packageJson);

  this.activeServiceMap_ = new Map();
  this.protos = {};

  var protoServices = config.protoServices;

  var self = this;

  Object.keys(protoServices).forEach(function(name) {
    var protoConfig = protoServices[name];
    var service = self.loadProtoFile_(protoConfig, config);

    self.protos[name] = service;

    if (protoConfig.baseUrl) {
      service.baseUrl = protoConfig.baseUrl;

this.grpcMetadata.add('x-goog-api-client', [
    'gl-node/' + process.versions.node,
    'gccl/' + config.packageJson.version,
    'grpc/' + require('grpc/package.json').version
  ].join(' '));

  if (config.grpcMetadata) {
    for (var prop in config.grpcMetadata) {
      if (config.grpcMetadata.hasOwnProperty(prop)) {
        this.grpcMetadata.add(prop, config.grpcMetadata[prop]);
      }
    }
  }

  this.maxRetries = options.maxRetries;
  this.userAgent = util.getUserAgentFromPackageJson(config.packageJson);

  this.activeServiceMap_ = new Map();
  this.protos = {};

  var protoServices = config.protoServices;

  var self = this;

  Object.keys(protoServices).forEach(function(name) {
    var protoConfig = protoServices[name];
    var service = self.loadProtoFile_(protoConfig, config);

    self.protos[name] = service;

    if (protoConfig.baseUrl) {
      service.baseUrl = protoConfig.baseUrl;