Avoid N^2 walk placing renderers when building the render tree

Source/core/dom/ContainerNode.h

Index: Source/core/dom/ContainerNode.h
diff --git a/Source/core/dom/ContainerNode.h b/Source/core/dom/ContainerNode.h
index 55c3bf4f55456da9294cc103f6e702a8001ec93c..c9b2030c2fba97489a122df59a3a324942689816 100644
--- a/Source/core/dom/ContainerNode.h
+++ b/Source/core/dom/ContainerNode.h
@@ -284,7 +284,7 @@ class ChildNodesLazySnapshot {
     WTF_MAKE_FAST_ALLOCATED;
 public:
     explicit ChildNodesLazySnapshot(Node* parentNode)
-        : m_currentNode(parentNode->firstChild())
+        : m_currentNode(parentNode->lastChild())
         , m_currentIndex(0)
     {
         m_nextSnapshot = latestSnapshot;
@@ -297,12 +297,12 @@ public:
     }
 
     // Returns 0 if there is no next Node.

[esprehn, 2013/06/05 00:12:26]

is no previous node?

-    PassRefPtr<Node> nextNode()
+    PassRefPtr<Node> previousNode()
     {
         if (LIKELY(!hasSnapshot())) {
             RefPtr<Node> node = m_currentNode;
             if (node)
-                m_currentNode = node->nextSibling();
+                m_currentNode = node->previousSibling();
             return node.release();
         }
         Vector<RefPtr<Node> >& nodeVector = *m_childNodes;
@@ -319,7 +319,7 @@ public:
         Node* node = m_currentNode.get();
         while (node) {
             m_childNodes->append(node);
-            node = node->nextSibling();
+            node = node->previousSibling();
         }
     }