Implement cloneNode for Document

LayoutTests/fast/dom/HTMLDocument/clone-node.html

+<!-- quirks mode -->
+<title>Tests HTMLDocument cloneNode</title>
+<link rel="help" href="http://dom.spec.whatwg.org/#dom-node-clonenode">
+<script src="../../js/resources/js-test-pre.js"></script>
+<script>
+description('Tests cloneNode for HTMLDocument.');
+
+function className(object) {
+    return Object.prototype.toString.call(object).slice(8, -1);
+}
+
+shouldBe('document.cloneNode(false).__proto__', 'HTMLDocument.prototype');
+shouldBeEqualToString('className(document.cloneNode(false))', 'HTMLDocument');
+shouldBe('document.cloneNode(true).title', 'document.title');
+shouldBeEqualToString('document.cloneNode(true).compatMode', 'BackCompat');
+
+var doc = document.implementation.createHTMLDocument('title');
+shouldBe('doc.cloneNode(false).__proto__', 'HTMLDocument.prototype');
+shouldBeEqualToString('className(doc.cloneNode(false))', 'HTMLDocument');
+shouldBe('doc.cloneNode(true).title', 'doc.title');
+shouldBeEqualToString('doc.cloneNode(true).compatMode', 'CSS1Compat');
+
+</script>
+<script src="../../js/resources/js-test-post.js"></script>
+</body>