Adapt and reland old position sticky implementation

third_party/WebKit/Source/core/layout/LayoutBox.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007 Apple 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 995 matching lines @@
     bool logicalHeightComputesAsNone(SizeType) const;
 
     bool isBox() const = delete; // This will catch anyone doing an unnecessary check.
 
     void frameRectChanged()
     {
         // The frame rect may change because of layout of other objects.
         // Should check this object for paint invalidation.
         if (!needsLayout())
             setMayNeedPaintInvalidation();
+        invalidateScrollAncestorConstraints();

[chrishtr, 2016/03/09 16:53:08]

Is this where you handle the case of an element with the same scroller as a
position-sticky element that may affect
the sticky constraints for that scroller?

Does the CL have a test for this scenario?

[flackr, 2016/03/14 19:04:26]

Yes.
It does now :-) - sticky-container-moved.html

[chrishtr, 2016/03/16 21:52:39]

Hmm. I'm trying to think of whether it is possible to not change the frame rect
but still screw things up. What if a transform is
changed on an element between the scroller and the sticky element?

How about instead always invalidating the sticky constraints for any containing
scroller whenever style or layout of any element changes? That should be
complete.

[flackr, 2016/03/22 21:44:32]

I'm fairly certain that transforms shouldn't be included in the sticky
constraints. Trying to include transforms would require also supporting
animations of transforms.

     }
 
     // Returns true if the box intersects the viewport visible to the user.
     bool intersectsVisibleViewport();
 
     bool hitTestChildren(HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction);
 
     void updateBackgroundAttachmentFixedStatusAfterStyleChange();
 
     // The CSS border box rect for this box.
@@ skipping 106 matching lines @@
         if (UNLIKELY(m_inlineBoxWrapper != nullptr))
             deleteLineBoxWrapper();
     }
 
     m_inlineBoxWrapper = boxWrapper;
 }
 
 } // namespace blink
 
 #endif // LayoutBox_h