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 b0bc6ed38731bbb1bda53c56c62643d6083660c5..0788dee631a4958fd22799571c48ff9ee6ebe741 100644
--- a/Source/core/layout/LayoutBox.cpp
+++ b/Source/core/layout/LayoutBox.cpp
@@ -1524,6 +1524,21 @@ LayoutUnit LayoutBox::shrinkLogicalWidthToAvoidFloats(LayoutUnit childMarginStar
     return width;
 }
 
+LayoutUnit LayoutBox::containingBlockLogicalHeightForGetComputedStyle() const
+{
+    if (hasOverrideContainingBlockLogicalHeight())
+        return overrideContainingBlockContentLogicalHeight();
+
+    if (!isPositioned())
+        return containingBlockLogicalHeightForContent(ExcludeMarginBorderPadding);
+
+    LayoutBoxModelObject* cb = toLayoutBoxModelObject(container());
+    LayoutUnit height = containingBlockLogicalHeightForPositioned(cb);
+    if (styleRef().position() != AbsolutePosition)
+        height -= cb->paddingLogicalHeight();
+    return height;
+}
+
 LayoutUnit LayoutBox::containingBlockLogicalWidthForContent() const
 {
     if (hasOverrideContainingBlockLogicalWidth())