Fix incorrect percentage top for positioned elements.

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 458 matching lines @@
     void deleteLineBoxWrapper();
 
     void setSpannerPlaceholder(LayoutMultiColumnSpannerPlaceholder&);
     void clearSpannerPlaceholder();
     virtual LayoutMultiColumnSpannerPlaceholder* spannerPlaceholder() const final { return m_rareData ? m_rareData->m_spannerPlaceholder : 0; }
 
     virtual LayoutRect clippedOverflowRectForPaintInvalidation(const LayoutBoxModelObject* paintInvalidationContainer, const PaintInvalidationState* = 0) const override;
     virtual void mapRectToPaintInvalidationBacking(const LayoutBoxModelObject* paintInvalidationContainer, LayoutRect&, const PaintInvalidationState*) const override;
     virtual void invalidatePaintForOverhangingFloats(bool paintAllDescendants);
 
+    LayoutUnit containingBlockLogicalHeightForGetComputedStyle() const;
+
     virtual LayoutUnit containingBlockLogicalWidthForContent() const override;
     LayoutUnit containingBlockLogicalHeightForContent(AvailableLogicalHeightType) const;
 
     LayoutUnit containingBlockAvailableLineWidth() const;
     LayoutUnit perpendicularContainingBlockLogicalHeight() const;
 
     virtual void updateLogicalWidth();
     void updateLogicalHeight();
     virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const;
 
@@ skipping 423 matching lines @@
         if (UNLIKELY(inlineBoxWrapper() != 0))
             deleteLineBoxWrapper();
     }
 
     ensureRareData().m_inlineBoxWrapper = boxWrapper;
 }
 
 } // namespace blink
 
 #endif // LayoutBox_h