Add ComposedTreeTraversal::lastWithin/lastWithinOrSelf

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 77 matching lines @@
     // 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
     // returns the number of the child nodes of the specified node in the
     // composed tree.
     static unsigned countChildren(const Node&);
 
+    static Node* lastWithin(const Node&);
+    static Node& lastWithinOrSelf(Node&);

[hayato, 2015/03/26 03:28:27]

Input |Node&| can't be |const Node&|?

I guess our concern is the case where it returns self, however, 
I think it's okay that |const Node&| will be discarded for self in this case in
practical.

[hajimehoshi, 2015/03/26 03:37:18]

As you mentioned, I was worried the case when this function returns the argument
itself. You mean I can use const_cast in this case? I'll try to do that.

[hajimehoshi, 2015/03/26 03:43:26]

Done.

+
 private:
     enum TraversalDirection {
         TraversalDirectionForward,
         TraversalDirectionBackward
     };
 
     static void assertPrecondition(const Node& node)
     {
 #if ENABLE(ASSERT)
         ASSERT(node.inDocument() ? !node.document().childNeedsDistributionRecalc() : !node.childNeedsDistributionRecalc());
@@ skipping 135 matching lines @@
 }
 
 inline Node* ComposedTreeTraversal::traverseLastChild(const Node& node)
 {
     return traverseChild(node, TraversalDirectionBackward);
 }
 
 } // namespace
 
 #endif