Fix squashing to treat perspective and preserve3d elements as transform ancestors.

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 36 matching lines @@
 #include "core/rendering/RenderImage.h"
 #include "core/rendering/RenderLayerStackingNodeIterator.h"
 #include "core/rendering/RenderPart.h"
 #include "core/rendering/RenderVideo.h"
 #include "core/rendering/RenderView.h"
 #include "core/rendering/compositing/RenderLayerCompositor.h"
 #include "core/rendering/style/KeyframeList.h"
 #include "platform/LengthFunctions.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/fonts/FontCache.h"
+#include "platform/geometry/TransformState.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/text/StringBuilder.h"
 
 namespace blink {
 
 using namespace HTMLNames;
 
 static IntRect clipBox(RenderBox* renderer);
 
@@ skipping 687 matching lines @@
 
     if (needsToReparentOverflowControls()) {
         if (m_overflowControlsClippingLayer) {
             m_overflowControlsClippingLayer->setPosition(m_ancestorClippingLayer->position());
             m_overflowControlsClippingLayer->setSize(m_ancestorClippingLayer->size());
             m_overflowControlsClippingLayer->setOffsetFromRenderer(m_ancestorClippingLayer->offsetFromRenderer());
             m_overflowControlsClippingLayer->setMasksToBounds(true);
 
             m_overflowControlsHostLayer->setPosition(IntPoint(-m_overflowControlsClippingLayer->offsetFromRenderer()));
         } else {
-            ASSERT(m_owningLayer.transformAncestor() == compositingStackingContext->transformAncestor());
-            LayoutPoint localOffsetToTransformedAncestor = m_owningLayer.computeOffsetFromTransformedAncestor();
-            LayoutPoint compositingStackingContextOffsetToTransformedAncestor = compositingStackingContext->computeOffsetFromTransformedAncestor();
-
-            m_overflowControlsHostLayer->setPosition(FloatPoint(localOffsetToTransformedAncestor - compositingStackingContextOffsetToTransformedAncestor));
+            // The controls are in the same 2D space as the compositing container, so we can map them into the space of the container.
+            TransformState transformState(TransformState::ApplyTransformDirection, FloatPoint());
+            m_owningLayer.renderer()->mapLocalToContainer(compositingStackingContext->renderer(), transformState, ApplyContainerFlip);
+            transformState.flatten();
+            LayoutPoint offsetFromStackingContainer = LayoutPoint(transformState.lastPlanarPoint());
+            m_overflowControlsHostLayer->setPosition(FloatPoint(offsetFromStackingContainer));
         }
     } else {
         m_overflowControlsHostLayer->setPosition(FloatPoint());
     }
 }
 
 void CompositedLayerMapping::updateChildContainmentLayerGeometry(const IntRect& clippingBox, const IntRect& localCompositingBounds)
 {
     if (!m_childContainmentLayer)
         return;
@@ skipping 1499 matching lines @@
     } else if (graphicsLayer == m_scrollingBlockSelectionLayer.get()) {
         name = "Scrolling Block Selection Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink