Add Traversal<*Element>::firstAncestor() API

Source/core/dom/ElementTraversal.h

Index: Source/core/dom/ElementTraversal.h
diff --git a/Source/core/dom/ElementTraversal.h b/Source/core/dom/ElementTraversal.h
index 6705f04efcd20b8bf281258b366a92797c59998a..e6d7e924ed65168990537f355f2588727990de9f 100644
--- a/Source/core/dom/ElementTraversal.h
+++ b/Source/core/dom/ElementTraversal.h
@@ -40,6 +40,11 @@ public:
     static ElementType* lastChild(const ContainerNode& current) { return lastChildTemplate(current); }
     static ElementType* lastChild(const Node& current) { return lastChildTemplate(current); }
 
+    // First ElementType ancestor of the node.
+    static ElementType* firstAncestor(const Node& current);
+    static ElementType* firstAncestorOrSelf(Node& current) { return firstAncestorOrSelfTemplate(current); }
+    static ElementType* firstAncestorOrSelf(Element& current) { return firstAncestorOrSelfTemplate(current); }
+
     // First or last ElementType descendant of the node.
     // For Elements firstWithin() is always the same as firstChild().
     static ElementType* firstWithin(const ContainerNode& current) { return firstWithinTemplate(current); }
@@ -81,6 +86,8 @@ private:
     template <class NodeType>
     static ElementType* lastChildTemplate(NodeType&);
     template <class NodeType>
+    static ElementType* firstAncestorOrSelfTemplate(NodeType&);
+    template <class NodeType>
     static ElementType* firstWithinTemplate(NodeType&);
     template <class NodeType>
     static ElementType* lastWithinTemplate(NodeType&);
@@ -167,6 +174,24 @@ inline ElementType* Traversal<ElementType>::firstChildTemplate(NodeType& current
 }
 
 template <class ElementType>
+inline ElementType* Traversal<ElementType>::firstAncestor(const Node& current)
+{
+    ContainerNode* ancestor = current.parentNode();
+    while (ancestor && !isElementOfType<const ElementType>(*ancestor))
+        ancestor = ancestor->parentNode();
+    return toElement<ElementType>(ancestor);
+}
+
+template <class ElementType>
+template <class NodeType>
+inline ElementType* Traversal<ElementType>::firstAncestorOrSelfTemplate(NodeType& current)
+{
+    if (isElementOfType<const ElementType>(current))
+        return &toElement<ElementType>(current);
+    return firstAncestor(current);
+}
+
+template <class ElementType>
 template <class NodeType>
 inline ElementType* Traversal<ElementType>::lastChildTemplate(NodeType& current)
 {