Correct the squashing origin w.r.t. the transformed ancestor to take into account rounding to integ…

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 533 matching lines @@
         // Store the local bounds of the RenderLayer subtree before applying the offset.
         layers[i].compositedBounds = squashedBounds;
 
         LayoutPoint offsetFromTransformedAncestorForSquashedLayer = layers[i].renderLayer->computeOffsetFromTransformedAncestor();
         LayoutSize offsetFromSquashingLayer = offsetFromTransformedAncestorForSquashedLayer - referenceOffsetFromTransformedAncestor;
 
         squashedBounds.move(offsetFromSquashingLayer);
         totalSquashBounds.unite(squashedBounds);
     }
 
-    *offsetFromTransformedAncestor = referenceOffsetFromTransformedAncestor;
-    offsetFromTransformedAncestor->moveBy(totalSquashBounds.location());
-
     // The totalSquashBounds is positioned with respect to referenceLayer of this CompositedLayerMapping.
     // But the squashingLayer needs to be positioned with respect to the ancestor CompositedLayerMapping.
     // The conversion between referenceLayer and the ancestor CLM is already computed as
     // offsetFromReferenceLayerToParentGraphicsLayer.
     totalSquashBounds.moveBy(offsetFromReferenceLayerToParentGraphicsLayer);
     IntRect squashLayerBounds = enclosingIntRect(totalSquashBounds);
     IntPoint squashLayerOrigin = squashLayerBounds.location();
     LayoutSize squashLayerOriginInOwningLayerSpace = squashLayerOrigin - offsetFromReferenceLayerToParentGraphicsLayer;
 
     squashingLayer->setPosition(squashLayerBounds.location());
     squashingLayer->setSize(squashLayerBounds.size());
 
+    *offsetFromTransformedAncestor = referenceOffsetFromTransformedAncestor;
+    offsetFromTransformedAncestor->move(squashLayerOriginInOwningLayerSpace);
+
     // Now that the squashing bounds are known, we can convert the RenderLayer painting offsets
     // from CLM owning layer space to the squashing layer space.
     //
     // The painting offset we want to compute for each squashed RenderLayer is essentially the position of
     // the squashed RenderLayer described w.r.t. referenceLayer's origin. For this purpose we already cached
     // offsetFromSquashingCLM before, which describes where the squashed RenderLayer is located w.r.t.
     // referenceLayer. So we just need to convert that point from referenceLayer space to referenceLayer
     // space. This is simply done by subtracing squashLayerOriginInOwningLayerSpace, but then the offset
     // overall needs to be negated because that's the direction that the painting code expects the
     // offset to be.
@@ skipping 1686 matching lines @@
     } else if (graphicsLayer == m_scrollingBlockSelectionLayer.get()) {
         name = "Scrolling Block Selection Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore