Implement ParentNode IDL interface

Source/core/dom/ContainerNode.h

Index: Source/core/dom/ContainerNode.h
diff --git a/Source/core/dom/ContainerNode.h b/Source/core/dom/ContainerNode.h
index e96dc0f1e7b3dbdb77ac168aebe47baf5a2b4226..b29abf70a9a65f8548f831e1d23432ad3c921fa1 100644
--- a/Source/core/dom/ContainerNode.h
+++ b/Source/core/dom/ContainerNode.h
@@ -33,7 +33,8 @@
 namespace WebCore {
 
 class FloatPoint;
-    
+class HTMLCollection;
+
 typedef void (*NodeCallback)(Node*, unsigned);
 
 namespace Private { 
@@ -86,6 +87,12 @@ public:
     Node* lastChild() const { return m_lastChild; }
     bool hasChildNodes() const { return m_firstChild; }
 
+    // ParentNode interface API
+    PassRefPtr<HTMLCollection> children();
+    Element* firstElementChild() const;
+    Element* lastElementChild() const;
+    unsigned childElementCount() const;
+
     unsigned childNodeCount() const;
     Node* childNode(unsigned index) const;