Prefer ComposedTreeTraversal to NodeRenderingTraversal.

Source/core/dom/shadow/ComposedTreeTraversal.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 66 matching lines @@
 
     // Composed tree version of |NodeTraversal::previousSkippingChildren()|
     // similar to |previous()| but skipping child nodes of the specified node.
     static Node* previousSkippingChildren(const Node&);
 
     // Composed tree version of |Node::isDescendantOf(other)|. This function
     // returns true if |other| contains |node|, otherwise returns
     // false. If |other| is |node|, this function returns false.
     static bool isDescendantOf(const Node& /*node*/, const Node& other);
 
+    static bool contains(const ContainerNode& container, const Node& node)
+    {
+        assertPrecondition(container);
+        assertPrecondition(node);
+        return container == node || isDescendantOf(node, container);
+    }
+
     // Returns a common ancestor of |nodeA| and |nodeB| if exists, otherwise
     // returns |nullptr|.
     static Node* commonAncestor(const Node& nodeA, const Node& nodeB);
 
     // Composed tree version of |Node::nodeIndex()|. This function returns a
     // zero base position number of the specified node in child nodes list, or
     // zero if the specified node has no parent.
     static unsigned index(const Node&);
 
     // Composed tree version of |ContainerNode::countChildren()|. This function
@@ skipping 194 matching lines @@
 }
 
 inline Node* ComposedTreeTraversal::traverseLastChild(const Node& node)
 {
     return traverseChild(node, TraversalDirectionBackward);
 }
 
 } // namespace
 
 #endif