Editorial: install private fields in default base constructor (#2462)

spec.html

@@ -24776,10 +24776,12 @@ <h1>
               1. NOTE: This branch behaves similarly to `constructor(...args) { super(...args); }`. The most notable distinction is that while the aforementioned ECMAScript source text observably calls the @@iterator method on `%Array.prototype%`, this function does not.
               1. Let _func_ be ! _F_.[[GetPrototypeOf]]().
               1. If IsConstructor(_func_) is *false*, throw a *TypeError* exception.
-              1. Return ? Construct(_func_, _args_, NewTarget).
+              1. Let _result_ be ? Construct(_func_, _args_, NewTarget).
             1. Else,
               1. NOTE: This branch behaves similarly to `constructor() {}`.
-              1. Return ? OrdinaryCreateFromConstructor(NewTarget, *"%Object.prototype%"*).
+              1. Let _result_ be ? OrdinaryCreateFromConstructor(NewTarget, *"%Object.prototype%"*).
+            1. Perform ? InitializeInstanceElements(_result_, _F_).
+            1. Return _result_.
           1. Let _F_ be ! CreateBuiltinFunction(_defaultConstructor_, 0, _className_, &laquo; [[ConstructorKind]], [[SourceText]] &raquo;, the current Realm Record, _constructorParent_).
         1. Else,
           1. Let _constructorInfo_ be ! DefineMethod of _constructor_ with arguments _proto_ and _constructorParent_.