Bug 1041510. Now that we merge and flatten display items bottom to top (instead of the reverse) move the scroll info layer to be on top of the other scrolled content so that it is still processed last. r=roc

layout/generic/nsGfxScrollFrame.cpp

@@ -2641,7 +2641,13 @@ ScrollFrameHelper::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
     // metadata about this scroll box to the compositor process.
     nsDisplayScrollInfoLayer* layerItem = new (aBuilder) nsDisplayScrollInfoLayer(
       aBuilder, mScrolledFrame, mOuter);
-    scrolledContent.BorderBackground()->AppendNewToBottom(layerItem);
+    nsDisplayList* positionedDescendants = scrolledContent.PositionedDescendants();
+    if (!positionedDescendants->IsEmpty()) {
+      layerItem->SetOverrideZIndex(MaxZIndexInList(positionedDescendants, aBuilder));
+      positionedDescendants->AppendNewToTop(layerItem);
+    } else {
+      aLists.Outlines()->AppendNewToTop(layerItem);
+    }
   }
   // Now display overlay scrollbars and the resizer, if we have one.
   AppendScrollPartsTo(aBuilder, aDirtyRect, scrolledContent,