Fix incorrect percentage top for positioned elements.

Source/core/layout/LayoutBox.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, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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 1503 matching lines @@
     // We need to see if margins on either the start side or the end side can contain the floats in question. If they can,
     // then just using the line width is inaccurate. In the case where a float completely fits, we don't need to use the line
     // offset at all, but can instead push all the way to the content edge of the containing block. In the case where the float
     // doesn't fit, we can use the line offset, but we need to grow it by the margin to reflect the fact that the margin was
     // "consumed" by the float. Negative margins aren't consumed by the float, and so we ignore them.
     width += portionOfMarginNotConsumedByFloat(childMarginStart, startOffsetForContent, startOffsetForLine);
     width += portionOfMarginNotConsumedByFloat(childMarginEnd, endOffsetForContent, endOffsetForLine);
     return width;
 }
 
+LayoutUnit LayoutBox::containingBlockLogicalHeight() const
+{
+    if (hasOverrideContainingBlockLogicalHeight())
+        return overrideContainingBlockContentLogicalHeight();
+
+    // http://www.w3.org/TR/CSS21/visudet.html#containing-block-details

[mstensho (USE GERRIT), 2015/03/26 12:53:37]

Better omit this text. This is not completely spec compliant, and it never was
(not before your changes, either).

Consider:
<span style="display:inline; position:relative;">
    xxx
    <div style="position:absolute; top:50%;">xxx</div>
</div>

It's laid out correctly, but computedStyle.top on the abspos won't use the
inline as its containing block. Not before your changes. Not after your changes.

[changseok, 2015/03/30 07:17:57]

Good point. containingBlock never return inline block. We might need an another
api to return containing box including inline block as well as layoutBlock e,g
containingBox()?

[changseok, 2015/03/30 18:03:34]

Well. we don't need to create a new api. container() works similarly.

+    LayoutBlock* cb = containingBlock();
+    LayoutUnit height = cb->isPositioned() ? containingBlockLogicalHeightForPositioned(cb) : cb->clientLogicalHeight();
+    if (styleRef().position() != AbsolutePosition)
+        height -= cb->paddingLogicalHeight();
+    return height;
+}
+
 LayoutUnit LayoutBox::containingBlockLogicalWidthForContent() const
 {
     if (hasOverrideContainingBlockLogicalWidth())
         return overrideContainingBlockContentLogicalWidth();
 
     LayoutBlock* cb = containingBlock();
     return cb->availableLogicalWidth();
 }
 
 LayoutUnit LayoutBox::containingBlockLogicalHeightForContent(AvailableLogicalHeightType heightType) const
@@ skipping 3107 matching lines @@
     computedValues.m_margins.m_end = marginEnd();
 
     setLogicalTop(oldLogicalTop);
     setLogicalWidth(oldLogicalWidth);
     setLogicalLeft(oldLogicalLeft);
     setMarginLeft(oldMarginLeft);
     setMarginRight(oldMarginRight);
 }
 
 } // namespace blink