Use LayoutObject to locate the flow thread.

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 586 matching lines @@
     bool attemptDirectCompositingUpdate(StyleDifference, const ComputedStyle* oldStyle);
     void updateTransform(const ComputedStyle* oldStyle, const ComputedStyle& newStyle);
 
     void dirty3DTransformedDescendantStatus();
     // Both updates the status, and returns true if descendants of this have 3d.
     bool update3DTransformedDescendantStatus();
 
     void updateOrRemoveFilterClients();
 
     void updatePaginationRecursive(bool needsPaginationUpdate = false);
-    void updatePagination();
     void clearPaginationRecursive();
 
     DeprecatedPaintLayerType m_layerType;
 
     // Self-painting layer is an optimization where we avoid the heavy Layer painting
     // machinery for a Layer allocated only to handle the overflow clip case.
     // FIXME(crbug.com/332791): Self-painting layer should be merged into the overflow-only concept.
     unsigned m_isSelfPaintingLayer : 1;
 
     // If have no self-painting descendants, we don't have to walk our children during painting. This can lead to
@@ skipping 99 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