Take padding into account during calculation of overflow constraining rect for sticky positioning.

Source/core/rendering/RenderBoxModelObject.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 326 matching lines @@
 
 LayoutSize RenderBoxModelObject::stickyPositionOffset() const
 {
     FloatRect constrainingRect;
 
     ASSERT(hasLayer());
     RenderLayer* enclosingClippingLayer = layer()->enclosingOverflowClipLayer(ExcludeSelf);
     if (enclosingClippingLayer) {
         RenderBox* enclosingClippingBox = toRenderBox(enclosingClippingLayer->renderer());
         LayoutRect clipRect = enclosingClippingBox->overflowClipRect(LayoutPoint(), 0); // FIXME: make this work in regions.
+        clipRect.move(enclosingClippingBox->paddingLeft(), enclosingClippingBox->paddingTop());

[ojan, 2014/02/19 20:03:24]

The equivalent webkit patch didn't have this
(https://bugs.webkit.org/attachment.cgi?id=224328&action=review). Can you
explain why this is needed?

[ostap, 2014/02/19 20:50:00]

Webkit takes padding into account for the position in
computeStickyPositionConstraints() .
That's because of this commit: http://trac.webkit.org/changeset/152998 
I don't think this change is relevant for chromium.

+        clipRect.contract(LayoutSize(enclosingClippingBox->paddingLeft() + enclosingClippingBox->paddingRight(),
+            enclosingClippingBox->paddingTop() + enclosingClippingBox->paddingBottom()));
         constrainingRect = enclosingClippingBox->localToContainerQuad(FloatRect(clipRect), view()).boundingBox();
     } else {
         LayoutRect viewportRect = view()->frameView()->viewportConstrainedVisibleContentRect();
         constrainingRect = viewportRect;
     }
 
     StickyPositionViewportConstraints constraints;
     computeStickyPositionConstraints(constraints, constrainingRect);
 
     // The sticky offset is physical, so we can just return the delta computed in absolute coords (though it may be wrong with transforms).
@@ skipping 2439 matching lines @@
     ASSERT(!beforeChild || toBoxModelObject == beforeChild->parent());
     for (RenderObject* child = startChild; child && child != endChild; ) {
         // Save our next sibling as moveChildTo will clear it.
         RenderObject* nextSibling = child->nextSibling();
         moveChildTo(toBoxModelObject, child, beforeChild, fullRemoveInsert);
         child = nextSibling;
     }
 }
 
 } // namespace WebCore