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

Source/core/dom/shadow/ShadowRoot.cpp

Index: Source/core/dom/shadow/ShadowRoot.cpp
diff --git a/Source/core/dom/shadow/ShadowRoot.cpp b/Source/core/dom/shadow/ShadowRoot.cpp
index 075eb774ce1ba8e4c09527736f4377c3c11e667e..d409799d1d8ce9af52521dc022ee2fa2afe7be5a 100644
--- a/Source/core/dom/shadow/ShadowRoot.cpp
+++ b/Source/core/dom/shadow/ShadowRoot.cpp
@@ -148,7 +148,7 @@ void ShadowRoot::recalcStyle(StyleChange change)
     StyleResolver* styleResolver = document()->styleResolver();
     styleResolver->pushParentShadowRoot(this);
 
-    for (Node* child = firstChild(); child; child = child->nextSibling()) {
+    for (Node* child = lastChild(); child; child = child->previousSibling()) {
         if (child->isElementNode())
             toElement(child)->recalcStyle(change);
         else if (child->isTextNode())