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

Source/core/rendering/compositing/CompositingLayerAssigner.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Google 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
@@ skipping 165 matching lines @@
             squashingState.mostRecentMapping->updateSquashingLayerAssignment(layer, squashingState.mostRecentMapping->owningLayer(), squashingState.nextSquashedLayerIndex);
         if (!changedSquashingLayer)
             return true;
 
         // If we've modified the collection of squashed layers, we must update
         // the graphics layer geometry.
         squashingState.mostRecentMapping->setNeedsGraphicsLayerUpdate();
 
         layer->clipper().clearClipRectsIncludingDescendants();
 
-        // If we need to repaint, do so before allocating the layer to the squashing layer.
-        m_compositor->repaintOnCompositingChange(layer);
-
         // FIXME: it seems premature to compute this before all compositing state has been updated?
         // This layer and all of its descendants have cached repaints rects that are relative to
         // the repaint container, so change when compositing changes; we need to update them here.
 
         // FIXME: what's up with parent()?
         if (layer->parent())
             layer->repainter().computeRepaintRectsIncludingDescendants();
 
+        // Issue a repaint, since |layer| may have been added to an already-existing squashing layer.
+        m_compositor->repaintOnCompositingChange(layer);
+
         return true;
     }
     if (compositedLayerUpdate == RemoveFromSquashingLayer) {
         if (layer->groupedMapping()) {
+            // Before removing |layer| from an already-existing squashing layer that may have other content, issue a repaint.
+            m_compositor->repaintOnCompositingChange(layer);
             layer->groupedMapping()->setNeedsGraphicsLayerUpdate();
             layer->setGroupedMapping(0);
         }
 
         // This layer and all of its descendants have cached repaints rects that are relative to
         // the repaint container, so change when compositing changes; we need to update them here.
         layer->repainter().computeRepaintRectsIncludingDescendants();
 
-        // If we need to repaint, do so now that we've removed it from a squashed layer
+        // If we need to repaint, do so now that we've removed it from a squashed layer.
         m_compositor->repaintOnCompositingChange(layer);
 
         layer->setLostGroupedMapping(false);
         return true;
     }
 
     return false;
 }
 
 void CompositingLayerAssigner::assignLayersToBackingsForReflectionLayer(RenderLayer* reflectionLayer, bool& layersChanged)
@@ skipping 52 matching lines @@
 
     RenderLayerStackingNodeIterator iterator(*layer->stackingNode(), NormalFlowChildren | PositiveZOrderChildren);
     while (RenderLayerStackingNode* curNode = iterator.next())
         assignLayersToBackingsInternal(curNode->layer(), squashingState, layersChanged);
 
     if (squashingState.hasMostRecentMapping && &squashingState.mostRecentMapping->owningLayer() == layer)
         squashingState.haveAssignedBackingsToEntireSquashingLayerSubtree = true;
 }
 
 }