Implement ParentNode IDL interface

Source/core/dom/DocumentFragment.idl

Index: Source/core/dom/DocumentFragment.idl
diff --git a/Source/core/dom/DocumentFragment.idl b/Source/core/dom/DocumentFragment.idl
index 0837e787ef90a0d4bd568b2223785a54caa2ea7d..01ca5de501444bcb90d901b71ba8d961f7b01ca0 100644
--- a/Source/core/dom/DocumentFragment.idl
+++ b/Source/core/dom/DocumentFragment.idl
@@ -25,5 +25,11 @@
     // NodeSelector - Selector API
     [RaisesException] Element querySelector(DOMString selectors);
     [RaisesException] NodeList querySelectorAll(DOMString selectors);
+
+    // ParentNode interface API
+    readonly attribute HTMLCollection children;
+    readonly attribute Element firstElementChild;
+    readonly attribute Element lastElementChild;
+    readonly attribute unsigned long childElementCount;
 };