Issue repaints before and after changing the squashing assignment of a RenderLayer.

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
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  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 2157 matching lines @@
     // NOTE: composited bounds are updated elsewhere
     // NOTE: offsetFromRenderer is updated elsewhere
     paintInfo.paintingPhase = GraphicsLayerPaintAllWithOverflowClip;
     paintInfo.isBackgroundLayer = false;
 
     // Change tracking on squashing layers: at the first sign of something changed, just invalidate the layer.
     // FIXME: Perhaps we can find a tighter more clever mechanism later.
     bool updatedAssignment = false;
     if (nextSquashedLayerIndex < m_squashedLayers.size()) {
         if (!paintInfo.isEquivalentForSquashing(m_squashedLayers[nextSquashedLayerIndex])) {
+            compositor()->repaintOnCompositingChange(squashedLayer);
             updatedAssignment = true;
             m_squashedLayers[nextSquashedLayerIndex] = paintInfo;
         }
     } else {
+        compositor()->repaintOnCompositingChange(squashedLayer);
         m_squashedLayers.append(paintInfo);
         updatedAssignment = true;
     }

[ojan, 2014/06/03 18:41:11]

Nit: you could write this as follows to avoid some minor code duplication:
if (updatedAssignment)
    compositor()->repaintOnCompositingChange(squashedLayer);

[chrishtr, 2014/06/03 20:47:08]

I'm doing it the current way because I want to have it happen before
m_squashedLayers is changed, because in principle that changes compositing
state.

     squashedLayer->setGroupedMapping(this);
     return updatedAssignment;
 }
 
 void CompositedLayerMapping::removeRenderLayerFromSquashingGraphicsLayer(const RenderLayer* layer)
 {
     size_t layerIndex = kNotFound;
 
     for (size_t i = 0; i < m_squashedLayers.size(); ++i) {
         if (m_squashedLayers[i].renderLayer == layer) {
@@ skipping 51 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore