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 2699 matching lines @@
     // FIXME: Check logicalTop/logicalBottom here to correctly handle vertical writing-mode.
     // https://bugs.webkit.org/show_bug.cgi?id=46500
     if (isLayoutBlock() && isOutOfFlowPositioned() && style()->height().isAuto() && !(style()->top().isAuto() || style()->bottom().isAuto())) {
         LayoutBlock* block = const_cast<LayoutBlock*>(toLayoutBlock(this));
         LogicalExtentComputedValues computedValues;
         block->computeLogicalHeight(block->logicalHeight(), 0, computedValues);
         LayoutUnit newContentHeight = computedValues.m_extent - block->borderAndPaddingLogicalHeight() - block->scrollbarLogicalHeight();
         return adjustContentBoxLogicalHeightForBoxSizing(newContentHeight);
     }
 
-    // FIXME: This is wrong if the containingBlock has a perpendicular writing mode.

[rune, 2015/03/16 13:34:03]

You removed this FIXME. Is it fixed?

-    LayoutUnit availableHeight = containingBlockLogicalHeightForContent(heightType);
-    if (heightType == ExcludeMarginBorderPadding) {
-        // FIXME: Margin collapsing hasn't happened yet, so this incorrectly removes collapsed margins.

[rune, 2015/03/16 13:34:03]

You removed this FIXME. Is it fixed?

-        availableHeight -= marginBefore() + marginAfter() + borderAndPaddingLogicalHeight();
-    }
+    const LayoutBlock* cb = isLayoutBlock() ? toLayoutBlock(this) : containingBlock();

[mstensho (USE GERRIT), 2015/03/23 14:27:55]

Pretending that we're our own containing block? This makes no sense.

As far as I can tell, the only thing you want to change is resolving percentage
top/bottom values from computedStyle, to increase browser interoperability. Then
I don't think this method should be changed at all, since it's also called
during layout. The changes here cause quite a few test regressions.

[changseok, 2015/03/26 07:12:04]

Agree. I looked into this area more. I don't know the history of
containingBlockLogicalHeight , but what I can tell you is it is too much complex
over its name. Actually containingBlockLogicalWidth works more simple.
containingBlockLogicalWidthForContent -> availableLogicalWidth -> 
contentLogicalWidth -> contentWidth

In the other hand.
containingBlockLogicalHeightForContent -> availableLogicalHeight ->
availableLogicalHeightUsing -> containingBlockLogicalHeightForContent -> ... ->
eventually the height of viewport returned where containingBlock is static or
relative or absolute.

So I think getting content height from containingBlockLogicalHeightForContent is
not proper. It might be originally designed for this purpose, but not anymore.
Fixing this method may not be a good idea as you pointed out. It has been used
some places and involved in layout. Rather, adding a new method returning
immediate containingBlock's content height or padding box height is better for
percentage top.

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

Yeah, but resolving percentage heights isn't as simple as resolving percentage
widths. If the containing block has auto height, for instance...

+    LayoutUnit availableHeight = cb->clientLogicalHeight();

[rune, 2015/03/16 13:34:03]

This seems quite different from containingBlockLogicalHeightForContent(). If the
need for this change can be observed as bugs, you should add some more
testcases.

I don't quite follow this. Some layout code owner should take over reviewing, I
think.

[changseok, 2015/03/26 07:12:04]

Yeah.. I think containingBlockLogicalHeightForContent is too complex to get
contentHeight of containing block. We might need a more simple method for it.
O.K Thanks anyway ;)

+    if (heightType == ExcludeMarginBorderPadding)
+        availableHeight -= paddingBefore() + paddingAfter();
+    else if (heightType == IncludeMarginBorderPadding)
+        availableHeight += marginBefore() + marginAfter() + borderBefore() + borderAfter();
     return availableHeight;
 }
 
 void LayoutBox::computeAndSetBlockDirectionMargins(const LayoutBlock* containingBlock)
 {
     LayoutUnit marginBefore;
     LayoutUnit marginAfter;
     computeMarginsForDirection(BlockDirection, containingBlock, containingBlockLogicalWidthForContent(), logicalHeight(), marginBefore, marginAfter,
         style()->marginBeforeUsing(containingBlock->style()),
         style()->marginAfterUsing(containingBlock->style()));
@@ skipping 1908 matching lines @@
     computedValues.m_margins.m_end = marginEnd();
 
     setLogicalTop(oldLogicalTop);
     setLogicalWidth(oldLogicalWidth);
     setLogicalLeft(oldLogicalLeft);
     setMarginLeft(oldMarginLeft);
     setMarginRight(oldMarginRight);
 }
 
 } // namespace blink