Revert of Revert of Put the squashing layer underneath the ancestor clipping layer if present.

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 860 matching lines @@
         m_scrollingContentsLayer->setOffsetFromRenderer(scrollingContentsOffset, GraphicsLayer::DontSetNeedsDisplay);
 
         if (m_foregroundLayer) {
             if (m_foregroundLayer->size() != m_scrollingContentsLayer->size())
                 m_foregroundLayer->setSize(m_scrollingContentsLayer->size());
             m_foregroundLayer->setNeedsDisplay();
             m_foregroundLayer->setOffsetFromRenderer(m_scrollingContentsLayer->offsetFromRenderer());
         }
     }
 
-    updateSquashingLayerGeometry(delta);
+    {
+        IntPoint squashingDelta(delta);
+        squashingDelta.moveBy(-graphicsLayerParentLocation);
+        updateSquashingLayerGeometry(squashingDelta);
+    }
 
     if (m_owningLayer.scrollableArea() && m_owningLayer.scrollableArea()->scrollsOverflow())
         m_owningLayer.scrollableArea()->positionOverflowControls();
 
     // We can't make this call in RenderLayerCompositor::allocateOrClearCompositedLayerMapping
     // since it depends on whether compAncestor draws content, which gets updated later.
     updateRequiresOwnBackingStoreForAncestorReasons(compAncestor);
 
     if (RuntimeEnabledFeatures::cssCompositingEnabled()) {
         updateLayerBlendMode(style);
@@ skipping 71 matching lines @@
     if (m_layerForHorizontalScrollbar)
         m_graphicsLayer->addChild(m_layerForHorizontalScrollbar.get());
     if (m_layerForVerticalScrollbar)
         m_graphicsLayer->addChild(m_layerForVerticalScrollbar.get());
     if (m_layerForScrollCorner)
         m_graphicsLayer->addChild(m_layerForScrollCorner.get());
 
     // The squashing containment layer, if it exists, becomes a no-op parent.
     if (m_squashingLayer) {
         ASSERT(compositor()->layerSquashingEnabled());
-        ASSERT(m_squashingContainmentLayer);
+        ASSERT((m_ancestorClippingLayer && !m_squashingContainmentLayer) || (!m_ancestorClippingLayer && m_squashingContainmentLayer));
 
-        m_squashingContainmentLayer->removeAllChildren();
-
-        if (m_ancestorClippingLayer)
-            m_squashingContainmentLayer->addChild(m_ancestorClippingLayer.get());
-        else
+        if (m_squashingContainmentLayer) {
+            m_squashingContainmentLayer->removeAllChildren();
             m_squashingContainmentLayer->addChild(m_graphicsLayer.get());
-
-        m_squashingContainmentLayer->addChild(m_squashingLayer.get());
+            m_squashingContainmentLayer->addChild(m_squashingLayer.get());
+        } else {
+            // The ancestor clipping layer is already set up and has m_graphicsLayer under it.
+            m_ancestorClippingLayer->addChild(m_squashingLayer.get());
+        }
     }
 }
 
 void CompositedLayerMapping::updateContentsRect()
 {
     m_graphicsLayer->setContentsRect(pixelSnappedIntRect(contentsBox()));
 }
 
 void CompositedLayerMapping::updateDrawsContent()
 {
@@ skipping 459 matching lines @@
     if (needsSquashingLayers) {
         ASSERT(compositor()->layerSquashingEnabled());
 
         if (!m_squashingLayer) {
             ASSERT(!m_squashingContainmentLayer);
 
             m_squashingLayer = createGraphicsLayer(CompositingReasonLayerForSquashingContents);
             m_squashingLayer->setDrawsContent(true);
 
             // FIXME: containment layer needs a new CompositingReason, CompositingReasonOverlap is not appropriate.
-            m_squashingContainmentLayer = createGraphicsLayer(CompositingReasonLayerForSquashingContainer);
+            if (!m_ancestorClippingLayer)
+                m_squashingContainmentLayer = createGraphicsLayer(CompositingReasonLayerForSquashingContainer);
             layersChanged = true;
         }
 
-        ASSERT(m_squashingLayer && m_squashingContainmentLayer);
+        ASSERT(m_squashingLayer);
     } else {
         if (m_squashingLayer) {
             m_squashingLayer->removeFromParent();
             m_squashingLayer = nullptr;
-            // FIXME: do we need to invalidate something here?
-
-            ASSERT(m_squashingContainmentLayer);
+            layersChanged = true;
+        }
+        if (m_squashingContainmentLayer) {
             m_squashingContainmentLayer->removeFromParent();
             m_squashingContainmentLayer = nullptr;
             layersChanged = true;
         }
-
         ASSERT(!m_squashingLayer && !m_squashingContainmentLayer);
     }
 
     return layersChanged;
 }
 
 GraphicsLayerPaintingPhase CompositedLayerMapping::paintingPhaseForPrimaryLayer() const
 {
     unsigned phase = 0;
     if (!m_backgroundLayer)
@@ skipping 674 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore