Fix incorrect percentage top for positioned elements.

Source/core/layout/LayoutBox.cpp

Index: Source/core/layout/LayoutBox.cpp
diff --git a/Source/core/layout/LayoutBox.cpp b/Source/core/layout/LayoutBox.cpp
index a24c390b55c02b4bb0875bc2132b7c71861930ea..9a5d728312dc88e0e84ada12c18c9feb467ecc6c 100644
--- a/Source/core/layout/LayoutBox.cpp
+++ b/Source/core/layout/LayoutBox.cpp
@@ -1521,6 +1521,19 @@ LayoutUnit LayoutBox::shrinkLogicalWidthToAvoidFloats(LayoutUnit childMarginStar
     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())