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

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index a068fbaa7edf738b5c1e7cb87a95bda7d0d02e44..312b18fcd515bfd1af7e7ff158e8f09bf7fd7266 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -1681,7 +1681,7 @@ void Document::recalcStyle(StyleChange change)
                 renderer()->setStyle(documentStyle.release());
         }
 
-        for (Node* n = firstChild(); n; n = n->nextSibling()) {
+        for (Node* n = lastChild(); n; n = n->previousSibling()) {
             if (!n->isElementNode())
                 continue;
             Element* element = toElement(n);