Don't allow position:sticky for table columns.

Source/core/rendering/RenderTableCol.h

 /*
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 72 matching lines @@
     virtual const char* renderName() const OVERRIDE { return "RenderTableCol"; }
     virtual bool isRenderTableCol() const OVERRIDE { return true; }
     virtual void updateFromElement() OVERRIDE;
     virtual void computePreferredLogicalWidths() OVERRIDE { ASSERT_NOT_REACHED(); }
 
     virtual void insertedIntoTree() OVERRIDE;
     virtual void willBeRemovedFromTree() OVERRIDE;
 
     virtual bool isChildAllowed(RenderObject*, RenderStyle*) const OVERRIDE;
     virtual bool canHaveChildren() const OVERRIDE;
-    virtual LayerType layerTypeRequired() const OVERRIDE { return NoLayer; }
+    virtual LayerType layerTypeRequired() const OVERRIDE
+    {
+        if (isStickyPositioned())

[Julien - ping for review, 2014/03/12 03:14:42]

columns are only style placeholder. That's the reason we never allocate a layer
for them. Could you explain why you feel this is the right fix (I may be missing
some context here)?

[ostap, 2014/03/12 05:26:24]

I think that table column can be sticky positioned. Is it right?

[Julien - ping for review, 2014/03/12 15:17:04]

Yes, it can but that doesn't mean that we should allow it! It wouldn't be the
first time we adjust the style to prevent some situation we don't want from
happening (see StyleAdjuster).

Back on the current change, I was asking why you took this approach because for
me it doesn't feel like the right fix. We disable RenderLayers on <col> because
they make no sense. On top of that, we don't have a solid answer whether sticky
requires a RenderLayer (e.g. position:relative doesn't)

[ostap, 2014/03/12 15:51:12]

Ok. I'll disable sticky support for table elements that don't create
RenderLayer.
I think because relative positioned elements don't change their offset
dynamically, but sticky do change based on scroll position of the related
scrollbox.

+            return NormalLayer;
+
+        return NoLayer;
+    }
 
     virtual LayoutRect clippedOverflowRectForRepaint(const RenderLayerModelObject* repaintContainer) const OVERRIDE;
     virtual void imageChanged(WrappedImagePtr, const IntRect* = 0) OVERRIDE;
 
     virtual void styleDidChange(StyleDifference, const RenderStyle* oldStyle) OVERRIDE;
 
     RenderTable* table() const;
 
     RenderObjectChildList m_children;
     unsigned m_span;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderTableCol, isRenderTableCol());
 
 }
 
 #endif