Split NonDocumentTypeChildNode from ChildNode

Source/core/dom/ChildNode.h

Index: Source/core/dom/ChildNode.h
diff --git a/Source/core/dom/ChildNode.h b/Source/core/dom/ChildNode.h
index 749e4be02c0cedf766a7261389ef1a7bd734a668..3c3b1f5b0560251ee311f174acf1ac75e3025a61 100644
--- a/Source/core/dom/ChildNode.h
+++ b/Source/core/dom/ChildNode.h
@@ -5,23 +5,12 @@
 #ifndef ChildNode_h
 #define ChildNode_h
 
-#include "core/dom/ElementTraversal.h"
 #include "core/dom/Node.h"
 
 namespace blink {
 
 class ChildNode {
 public:
-    static Element* previousElementSibling(Node& node)
-    {
-        return ElementTraversal::previousSibling(node);
-    }
-
-    static Element* nextElementSibling(Node& node)
-    {
-        return ElementTraversal::nextSibling(node);
-    }
-
     static void remove(Node& node, ExceptionState& exceptionState)
     {
         return node.remove(exceptionState);