Clear the groupedMapping parameter in layers when removed from the group

Source/core/paint/DeprecatedPaintLayer.h

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 298 matching lines @@
     GraphicsLayer* graphicsLayerBacking() const;
     GraphicsLayer* graphicsLayerBackingForScrolling() const;
     // NOTE: If you are using hasCompositedDeprecatedPaintLayerMapping to determine the state of compositing for this layer,
     // (and not just to do bookkeeping related to the mapping like, say, allocating or deallocating a mapping),
     // then you may have incorrect logic. Use compositingState() instead.
     // FIXME: This is identical to null checking compositedDeprecatedPaintLayerMapping(), why not just call that?
     bool hasCompositedDeprecatedPaintLayerMapping() const { return m_compositedDeprecatedPaintLayerMapping.get(); }
     void ensureCompositedDeprecatedPaintLayerMapping();
     void clearCompositedDeprecatedPaintLayerMapping(bool layerBeingDestroyed = false);
     CompositedDeprecatedPaintLayerMapping* groupedMapping() const { return m_groupedMapping; }
-    void setGroupedMapping(CompositedDeprecatedPaintLayerMapping* groupedMapping, bool layerBeingDestroyed = false);
+    void setGroupedMapping(CompositedDeprecatedPaintLayerMapping* groupedMapping, bool issueInvalidations);

[Ian Vollick, 2015/07/02 17:28:59]

Could you please use an enum rather than a boolean? I was confused at the
callsites and meaningful 2nd parameter would have really helped.

 
     bool hasCompositedMask() const;
     bool hasCompositedClippingMask() const;
     bool needsCompositedScrolling() const { return m_scrollableArea && m_scrollableArea->needsCompositedScrolling(); }
 
     // Computes the position of the given layout object in the space of |paintInvalidationContainer|.
     // FIXME: invert the logic to have paint invalidation containers take care of painting objects into them, rather than the reverse.
     // This will allow us to clean up this static method messiness.
     static LayoutPoint positionFromPaintInvalidationBacking(const LayoutObject*, const LayoutBoxModelObject* paintInvalidationContainer, const PaintInvalidationState* = 0);
 
@@ skipping 383 matching lines @@
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const blink::DeprecatedPaintLayer*);
 void showLayerTree(const blink::LayoutObject*);
 #endif
 
 #endif // Layer_h