[New multicol] Make -webkit-column-break-inside:avoid work.

Source/core/rendering/RenderBlock.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. 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
  * License as published by the Free Software Foundation; either
@@ skipping 5156 matching lines @@
             remainingHeight = intMod(remainingHeight, pageLogicalHeight);
         }
         return remainingHeight;
     }
 
     return flowThread->pageRemainingLogicalHeightForOffset(offset, pageBoundaryRule);
 }
 
 LayoutUnit RenderBlock::adjustForUnsplittableChild(RenderBox* child, LayoutUnit logicalOffset, bool includeMargins)
 {
-    bool checkColumnBreaks = view()->layoutState()->isPaginatingColumns();
+    bool checkColumnBreaks = view()->layoutState()->isPaginatingColumns() || flowThreadContainingBlock();
     bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->m_pageLogicalHeight;
     bool isUnsplittable = child->isUnsplittableForPagination() || (checkColumnBreaks && child->style()->columnBreakInside() == PBAVOID)
         || (checkPageBreaks && child->style()->pageBreakInside() == PBAVOID);
     if (!isUnsplittable)
         return logicalOffset;
     LayoutUnit childLogicalHeight = logicalHeightForChild(child) + (includeMargins ? marginBeforeForChild(child) + marginAfterForChild(child) : LayoutUnit());
     LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
     updateMinimumPageHeight(logicalOffset, childLogicalHeight);
     if (!pageLogicalHeight || childLogicalHeight > pageLogicalHeight)
         return logicalOffset;
@@ skipping 298 matching lines @@
 void RenderBlock::showLineTreeAndMark(const InlineBox* markedBox1, const char* markedLabel1, const InlineBox* markedBox2, const char* markedLabel2, const RenderObject* obj) const
 {
     showRenderObject();
     for (const RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox())
         root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj, 1);
 }
 
 #endif
 
 } // namespace WebCore