Issue repaints when offsetFromRenderer changes for any squashed layer.

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 559 matching lines @@
     // 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.
     for (size_t i = 0; i < layers.size(); ++i) {
         LayoutPoint offsetFromTransformedAncestorForSquashedLayer = layers[i].renderLayer->computeOffsetFromTransformedAncestor();
         LayoutSize offsetFromSquashLayerOrigin = (offsetFromTransformedAncestorForSquashedLayer - referenceOffsetFromTransformedAncestor) - squashLayerOriginInOwningLayerSpace;
-        layers[i].offsetFromRenderer = -flooredIntSize(offsetFromSquashLayerOrigin);
+
+        // It is ok to repaint here, because all of the geometry needed to correctly repaint is computed by this point.
+        IntSize newOffsetFromRenderer = -flooredIntSize(offsetFromSquashLayerOrigin);
+        if (layers[i].offsetFromRendererSet && layers[i].offsetFromRenderer != newOffsetFromRenderer)
+            layers[i].renderLayer->repainter().repaintIncludingNonCompositingDescendants();
+        layers[i].offsetFromRenderer = newOffsetFromRenderer;
+        layers[i].offsetFromRendererSet = true;
 
         layers[i].renderLayer->setSubpixelAccumulation(offsetFromSquashLayerOrigin.fraction());
         ASSERT(layers[i].renderLayer->subpixelAccumulation() ==
             toLayoutSize(computeOffsetFromCompositedAncestor(layers[i].renderLayer, layers[i].renderLayer->ancestorCompositingLayer())).fraction());
 
         // FIXME: find a better design to avoid this redundant value - most likely it will make
         // sense to move the paint task info into RenderLayer's m_compositingProperties.
         layers[i].renderLayer->setOffsetFromSquashingLayerOrigin(layers[i].offsetFromRenderer);
-
     }
 
     for (size_t i = 0; i < layers.size(); ++i)
         layers[i].localClipRectForSquashedLayer = localClipRectForSquashedLayer(referenceLayer, layers[i], layers);
 }
 
 void CompositedLayerMapping::updateGraphicsLayerGeometry(GraphicsLayerUpdater::UpdateType updateType, const RenderLayer* compositingContainer)
 {
     if (!shouldUpdateGraphicsLayer(updateType))
         return;
@@ skipping 1612 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore