Update scroll parent correctly for squashing layers.

Source/core/rendering/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 445 matching lines @@
 
     if (updateForegroundLayer(compositor->needsContentsCompositingLayer(&m_owningLayer)))
         layerConfigChanged = true;
 
     bool needsDescendentsClippingLayer = compositor->clipsCompositingDescendants(&m_owningLayer);
 
     // Our scrolling layer will clip.
     if (m_owningLayer.needsCompositedScrolling())
         needsDescendentsClippingLayer = false;
 
+    // FIXME: this should not be computed dynamically, but passed down during the compositing update.
+    // See http://crbug.com/351851
     RenderLayer* scrollParent = m_owningLayer.scrollParent();
     bool needsAncestorClip = compositor->clippedByAncestor(&m_owningLayer);
     if (scrollParent) {
         // If our containing block is our ancestor scrolling layer, then we'll already be clipped
         // to it via our scroll parent and we don't need an ancestor clipping layer.
         if (m_owningLayer.renderer()->containingBlock()->enclosingLayer() == m_owningLayer.ancestorCompositedScrollingLayer())
             needsAncestorClip = false;
     }
 
     if (updateClippingLayers(needsAncestorClip, needsDescendentsClippingLayer))
@@ skipping 387 matching lines @@
 
     updateHasGpuRasterizationHint(renderer()->style());
     updateContentsRect();
     updateBackgroundColor();
     updateDrawsContent();
     updateContentsOpaque();
     updateAfterWidgetResize();
     updateRenderingContext();
     updateShouldFlattenTransform();
     updateChildrenTransform();
+    // FIXME: this should not be computed dynamically, but passed down during the compositing update.
+    // See http://crbug.com/351851
+    updateScrollParent(m_owningLayer.scrollParent());
     registerScrollingLayers();
 
     updateCompositingReasons();
 
     return updateType;
 }
 
 void CompositedLayerMapping::registerScrollingLayers()
 {
     // Register fixed position layers and their containers with the scrolling coordinator.
@@ skipping 506 matching lines @@
 
     // Only the topmost layer has a scroll parent. All other layers have a null scroll parent.
     if (layer != topmostLayer)
         scrollParent = 0;
 
     scrollingCoordinator->updateScrollParentForGraphicsLayer(layer, scrollParent);
 }
 
 void CompositedLayerMapping::updateScrollParent(RenderLayer* scrollParent)
 {
+    if (!scrollParent && m_squashedLayers.size())
+        scrollParent = m_squashedLayers[0].renderLayer->scrollParent();
 
     if (ScrollingCoordinator* scrollingCoordinator = scrollingCoordinatorFromLayer(m_owningLayer)) {
-        GraphicsLayer* topmostLayer = localRootForOwningLayer();
+        GraphicsLayer* topmostLayer = childForSuperlayers();
+        updateScrollParentForGraphicsLayer(m_squashingContainmentLayer.get(), topmostLayer, scrollParent, scrollingCoordinator);
         updateScrollParentForGraphicsLayer(m_ancestorClippingLayer.get(), topmostLayer, scrollParent, scrollingCoordinator);
         updateScrollParentForGraphicsLayer(m_graphicsLayer.get(), topmostLayer, scrollParent, scrollingCoordinator);
     }
 }
 
 void CompositedLayerMapping::updateClipParent(RenderLayer* clipParent)
 {
     if (ScrollingCoordinator* scrollingCoordinator = scrollingCoordinatorFromLayer(m_owningLayer))
         scrollingCoordinator->updateClipParentForGraphicsLayer(m_graphicsLayer.get(), clipParent);
 }
@@ skipping 713 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore