Issue invalidations when squashed layers move later or off of a grouped mapping.

Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.h

 /*
  * 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 283 matching lines @@
     static IntRect localClipRectForSquashedLayer(const DeprecatedPaintLayer& referenceLayer, const GraphicsLayerPaintInfo&,  const Vector<GraphicsLayerPaintInfo>& layers);
 
     // Return true if |m_owningLayer|'s compositing ancestor is not a descendant (inclusive) of the
     // clipping container for |m_owningLayer|.
     bool owningLayerClippedByLayerNotAboveCompositedAncestor(DeprecatedPaintLayer* scrollParent);
 
     DeprecatedPaintLayer* scrollParent();
 
     // Clear the groupedMapping entry on the layer at the given index, only if that layer does
     // not appear earlier in the set of layers for this object.
-    void clearLayerGroupingIfNoPrecedingEntry(size_t);
+    bool invalidateLayerIfNoPrecedingEntry(size_t);
 
     DeprecatedPaintLayer& m_owningLayer;
 
     // The hierarchy of layers that is maintained by the CompositedDeprecatedPaintLayerMapping looks like this:
     //
     //  + m_ancestorClippingLayer [OPTIONAL]
     //    + m_graphicsLayer
     //      + m_childTransformLayer [OPTIONAL]
     //      | + m_childContainmentLayer [OPTIONAL] <-OR-> m_scrollingLayer [OPTIONAL]
     //      |                                             + m_scrollingContentsLayer [Present iff m_scrollingLayer is present]
@@ skipping 108 matching lines @@
     unsigned m_pendingUpdateScope : 2;
     unsigned m_isMainFrameLayoutViewLayer : 1;
 
     unsigned m_backgroundLayerPaintsFixedRootBackground : 1;
     unsigned m_scrollingContentsAreEmpty : 1;
 };
 
 } // namespace blink
 
 #endif // CompositedDeprecatedPaintLayerMapping_h