url: use internal/util's getConstructorOf

PR-URL: #12526
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/url.js

@@ -5,6 +5,7 @@ const {
   hexTable,
   isHexTable
 } = require('internal/querystring');
+const { getConstructorOf } = require('internal/util');
 const binding = process.binding('url');
 const context = Symbol('context');
 const cannotBeBase = Symbol('cannot-be-base');
@@ -171,17 +172,6 @@ function onParseHashComplete(flags, protocol, username, password,
   this[context].fragment = fragment;
 }
 
-function getEligibleConstructor(obj) {
-  while (obj !== null) {
-    if (Object.prototype.hasOwnProperty.call(obj, 'constructor') &&
-        typeof obj.constructor === 'function') {
-      return obj.constructor;
-    }
-    obj = Object.getPrototypeOf(obj);
-  }
-  return null;
-}
-
 class URL {
   constructor(input, base) {
     // toUSVString is not needed.
@@ -220,7 +210,7 @@ class URL {
     if (typeof depth === 'number' && depth < 0)
       return opts.stylize('[Object]', 'special');
 
-    const ctor = getEligibleConstructor(this);
+    const ctor = getConstructorOf(this);
 
     const obj = Object.create({
       constructor: ctor === null ? URL : ctor