Don't rely on values computed as a side effect of paint.

Source/core/rendering/RenderLayer.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 181 matching lines @@
 
     void updateTransform();
     void update3dRenderingContext();
     RenderLayer* renderingContextRoot() const { return m_3dRenderingContextRoot; }
 
     const LayoutSize& offsetForInFlowPosition() const { return m_offsetForInFlowPosition; }
 
     void addBlockSelectionGapsBounds(const LayoutRect&);
     void clearBlockSelectionGapsBounds();
     void repaintBlockSelectionGaps();
-    bool hasBlockSelectionGapBounds() const;
 
     RenderLayerStackingNode* stackingNode() { return m_stackingNode.get(); }
     const RenderLayerStackingNode* stackingNode() const { return m_stackingNode.get(); }
 
     bool subtreeIsInvisible() const { return !hasVisibleContent() && !hasVisibleDescendant(); }
 
     // FIXME: We should ASSERT(!m_visibleContentStatusDirty) here, but see https://bugs.webkit.org/show_bug.cgi?id=71044
     // ditto for hasVisibleDescendant(), see https://bugs.webkit.org/show_bug.cgi?id=71277
     bool hasVisibleContent() const { return m_hasVisibleContent; }
     bool hasVisibleDescendant() const { return m_hasVisibleDescendant; }
@@ skipping 583 matching lines @@
 
 } // namespace WebCore
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const WebCore::RenderLayer*);
 void showLayerTree(const WebCore::RenderObject*);
 #endif
 
 #endif // RenderLayer_h