Update scroll parent correctly for squashing layers.

Source/core/rendering/CompositedLayerMapping.cpp

Index: Source/core/rendering/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/CompositedLayerMapping.cpp b/Source/core/rendering/CompositedLayerMapping.cpp
index 87abdddafedbdc97184e9b9588f382c81c0bb2fd..f37a9e1acd132e6176b3304058ac5fa21b5cb0ff 100644
--- a/Source/core/rendering/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/CompositedLayerMapping.cpp
@@ -861,6 +861,7 @@ void CompositedLayerMapping::updateGraphicsLayerGeometry()
     updateRenderingContext();
     updateShouldFlattenTransform();
     updateChildrenTransform();
+    updateScrollParent(m_owningLayer->scrollParent());
     registerScrollingLayers();
 
     updateCompositingReasons();
@@ -1364,7 +1365,8 @@ void CompositedLayerMapping::updateScrollParent(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);
     }