Move sticky position constraints update to the pre-paint tree walk.

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 749 matching lines @@
       layer()->ancestorOverflowLayer()->getScrollableArea();
   StickyPositionScrollingConstraints constraints;
   FloatSize skippedContainersOffset;
   LayoutBlock* containingBlock = this->containingBlock();
   // Skip anonymous containing blocks.
   while (containingBlock->isAnonymous()) {
     skippedContainersOffset +=
         toFloatSize(FloatPoint(containingBlock->frameRect().location()));
     containingBlock = containingBlock->containingBlock();
   }
+
   LayoutBox* scrollAncestor =
       layer()->ancestorOverflowLayer()->isRootLayer()
           ? nullptr
           : toLayoutBox(layer()->ancestorOverflowLayer()->layoutObject());
 
   LayoutUnit maxContainerWidth =
       containingBlock->isLayoutView()
           ? containingBlock->logicalWidth()
           : containingBlock->containingBlockLogicalWidthForContent();
   // Sticky positioned element ignore any override logical width on the
@@ skipping 547 matching lines @@
   if (rootElementStyle->hasBackground())
     return false;
 
   if (node() != document().firstBodyElement())
     return false;
 
   return true;
 }
 
 }  // namespace blink