Handle percent height children of multicol containers correctly.

Source/core/rendering/RenderBox.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 2669 matching lines @@
     }
     if (height.isFixed())
         return height.value();
     if (height.isPercent())
         return computePercentageLogicalHeight(height);
     return -1;
 }
 
 bool RenderBox::skipContainingBlockForPercentHeightCalculation(const RenderBox* containingBlock) const
 {
+    // Flow threads for multicol or paged overflow should be skipped. They are invisible to the DOM,
+    // and percent heights of children should be resolved against the multicol or paged container.
+    if (containingBlock->isRenderFlowThread())
+        return true;
+
     // For quirks mode and anonymous blocks, we skip auto-height containingBlocks when computing percentages.
     // For standards mode, we treat the percentage as auto if it has an auto-height containing block.
     if (!document().inQuirksMode() && !containingBlock->isAnonymousBlock())
         return false;
     return !containingBlock->isTableCell() && !containingBlock->isOutOfFlowPositioned() && containingBlock->style()->logicalHeight().isAuto() && isHorizontalWritingMode() == containingBlock->isHorizontalWritingMode();
 }
 
 LayoutUnit RenderBox::computePercentageLogicalHeight(const Length& height) const
 {
     LayoutUnit availableHeight = -1;
@@ skipping 1990 matching lines @@
         return 0;
 
     if (!layoutState && !flowThreadContainingBlock())
         return 0;
 
     RenderBlock* containerBlock = containingBlock();
     return containerBlock->offsetFromLogicalTopOfFirstPage() + logicalTop();
 }
 
 } // namespace WebCore