Merge 136554

Source/WebCore/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 942 matching lines @@
     const LayoutRect borderBox = toRenderBox(renderer())->borderBoxRect();
     RenderStyle* style = renderer()->style();
 
     return FloatPoint(floatValueForLength(style->perspectiveOriginX(), borderBox.width()),
                       floatValueForLength(style->perspectiveOriginY(), borderBox.height()));
 }
 
 RenderLayer* RenderLayer::stackingContext() const
 {
     RenderLayer* layer = parent();
-    while (layer && !layer->isRootLayer() && !layer->renderer()->isRoot() && layer->renderer()->style()->hasAutoZIndex())
+    while (layer && !layer->isStackingContext())
         layer = layer->parent();
+
+    ASSERT(!layer || layer->isStackingContext());
     return layer;
 }
 
 static inline bool isPositionedContainer(RenderLayer* layer)
 {
     RenderLayerModelObject* layerRenderer = layer->renderer();
     return layer->isRootLayer() || layerRenderer->isPositioned() || layer->hasTransform();
 }
 
 static inline bool isFixedPositionedContainer(RenderLayer* layer)
@@ skipping 4166 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif