Merge 136554

Source/WebCore/rendering/RenderLayer.cpp

Index: Source/WebCore/rendering/RenderLayer.cpp
===================================================================
--- Source/WebCore/rendering/RenderLayer.cpp	(revision 137695)
+++ Source/WebCore/rendering/RenderLayer.cpp	(working copy)
@@ -960,8 +960,10 @@
 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;
 }