update3dRenderingContext is 13.5% of GraphicsLayerUpdater::rebuildTree

Source/core/rendering/RenderObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 507 matching lines @@
     // Step 4: If |checkParent| is set, climb up to our parent and check its siblings that
     // follow us to see if we can locate a layer.
     if (checkParent && parent())
         return parent()->findNextLayer(parentLayer, this, true);
 
     return 0;
 }
 
 RenderLayer* RenderObject::enclosingLayer() const
 {
-    const RenderObject* curr = this;
-    while (curr) {
-        RenderLayer* layer = curr->hasLayer() ? toRenderLayerModelObject(curr)->layer() : 0;
-        if (layer)
-            return layer;
-        curr = curr->parent();
+    for (const RenderObject* current = this; current; current = current->parent()) {
+        if (current->hasLayer())
+            return toRenderLayerModelObject(current)->layer();
     }
+    // This line of code should be unreachable. However, if |this| is zero, we
+    // can reach this line. Of course, it's undefined behavior to call a member
+    // function on a zero pointer, but that doesn't stop
+    // FrameView::paintContents. :)
     return 0;
 }
 
 bool RenderObject::scrollRectToVisible(const LayoutRect& rect, const ScrollAlignment& alignX, const ScrollAlignment& alignY)
 {
     RenderBox* enclosingBox = this->enclosingBox();
     if (!enclosingBox)
         return false;
 
     enclosingBox->scrollRectToVisible(rect, alignX, alignY);
@@ skipping 2863 matching lines @@
 {
     if (object1) {
         const WebCore::RenderObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showRenderTreeAndMark(object1, "*", object2, "-", 0);
     }
 }
 
 #endif