url: use a class for WHATWG url[context]

The object is used as a structure, not as a map, which `StorageObject`
was designed for.

PR-URL: #12507
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/url.js

@@ -3,8 +3,7 @@
 const util = require('util');
 const {
   hexTable,
-  isHexTable,
-  StorageObject
+  isHexTable
 } = require('internal/querystring');
 const binding = process.binding('url');
 const context = Symbol('context');
@@ -97,6 +96,26 @@ class TupleOrigin {
   }
 }
 
+// This class provides the internal state of a URL object. An instance of this
+// class is stored in every URL object and is accessed internally by setters
+// and getters. It roughly corresponds to the concept of a URL record in the
+// URL Standard, with a few differences. It is also the object transported to
+// the C++ binding.
+// Refs: https://url.spec.whatwg.org/#concept-url
+class URLContext {
+  constructor() {
+    this.flags = 0;
+    this.scheme = undefined;
+    this.username = undefined;
+    this.password = undefined;
+    this.host = undefined;
+    this.port = undefined;
+    this.path = [];
+    this.query = undefined;
+    this.fragment = undefined;
+  }
+}
+
 function onParseComplete(flags, protocol, username, password,
                          host, port, path, query, fragment) {
   var ctx = this[context];
@@ -125,7 +144,7 @@ function onParseError(flags, input) {
 // Reused by URL constructor and URL#href setter.
 function parse(url, input, base) {
   const base_context = base ? base[context] : undefined;
-  url[context] = new StorageObject();
+  url[context] = new URLContext();
   binding.parse(input.trim(), -1,
                 base_context, undefined,
                 onParseComplete.bind(url), onParseError);