Implement a part of ProcessingInstruction by using PrivateScript

Source/core/xml/DocumentXSLT.js

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+"use strict";
+
+installClass("Document", function(DocumentPrototype) {
+    DocumentPrototype.xsltTransformed = function() {
+        return this.transformSourceDocument_;
+    }
+
+    DocumentPrototype.setTransformSourceDocument = function(document) {
+        this.transformSourceDocument_ = document;
+    }
+});