Fix incorrect percentage top for positioned elements.

Source/core/css/LayoutStyleCSSValueMapping.cpp

 /*
  * Copyright (C) 2004 Zack Rusin <zack@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2011 Sencha, Inc. All rights reserved.
  * Copyright (C) 2015 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ skipping 145 matching lines @@
         offset = style.top();
         break;
     case CSSPropertyBottom:
         offset = style.bottom();
         break;
     default:
         return nullptr;
     }
 
     if (offset.isPercent() && renderer && renderer->isBox()) {
+        // http://www.w3.org/TR/CSS21/visudet.html#containing-block-details
+        AvailableLogicalHeightType heightType = (style.position() == AbsolutePosition) ? IncludePadding : ExcludeMarginBorderPadding;
         LayoutUnit containingBlockSize = (propertyID == CSSPropertyLeft || propertyID == CSSPropertyRight) ?
             toLayoutBox(renderer)->containingBlockLogicalWidthForContent() :
-            toLayoutBox(renderer)->containingBlockLogicalHeightForContent(ExcludeMarginBorderPadding);
+            toLayoutBox(renderer)->containingBlockLogicalHeightForContent(heightType);
         return zoomAdjustedPixelValue(valueForLength(offset, containingBlockSize), style);
     }
     if (offset.isAuto()) {
         // FIXME: It's not enough to simply return "auto" values for one offset if the other side is defined.
         // In other words if left is auto and right is not auto, then left's computed value is negative right().
         // So we should get the opposite length unit and see if it is auto.
         return cssValuePool().createIdentifierValue(CSSValueAuto);
     }
 
     return zoomAdjustedPixelValueForLength(offset, style);
@@ skipping 2387 matching lines @@
         return zoomAdjustedPixelValueForLength(svgStyle.ry(), style);
 
     case CSSPropertyAll:
         return nullptr;
     }
     ASSERT_NOT_REACHED();
     return nullptr;
 }
 
 }