Add ComposedTreeTraversal::lastWithin/lastWithinOrSelf

Source/core/dom/shadow/ComposedTreeTraversal.cpp

 /*
  * 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 223 matching lines @@
 
 unsigned ComposedTreeTraversal::countChildren(const Node& node)
 {
     assertPrecondition(node);
     unsigned count = 0;
     for (Node* runner = traverseFirstChild(node); runner; runner = traverseNextSibling(*runner))
         ++count;
     return count;
 }
 
+Node* ComposedTreeTraversal::lastWithin(const Node& node)
+{
+    assertPrecondition(node);
+    Node* descendant = traverseLastChild(node);
+    for (Node* child = descendant; child; child = lastChild(*child))
+        descendant = child;
+    assertPostcondition(descendant);
+    return descendant;
+}
+
+Node& ComposedTreeTraversal::lastWithinOrSelf(const Node& node)
+{
+    assertPrecondition(node);
+    Node* lastDescendant = lastWithin(node);
+    Node& result = lastDescendant ? *lastDescendant : const_cast<Node&>(node);
+    assertPostcondition(&result);
+    return result;
+}
+
 } // namespace