[New Multicolumn] Only the nearest ancestral flow thread may serve as a containing flow thread.

Source/core/layout/LayoutState.cpp

 /*
  * Copyright (C) 2007 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 34 matching lines @@
     ASSERT(!view.layoutState());
     view.pushLayoutState(*this);
 }
 
 LayoutState::LayoutState(LayoutBox& renderer, const LayoutSize& offset, LayoutUnit pageLogicalHeight, bool pageLogicalHeightChanged, ColumnInfo* columnInfo, bool containingBlockLogicalWidthChanged)
     : m_containingBlockLogicalWidthChanged(containingBlockLogicalWidthChanged)
     , m_columnInfo(columnInfo)
     , m_next(renderer.view()->layoutState())
     , m_renderer(renderer)
 {
-    m_flowThread = renderer.isLayoutFlowThread() ? toLayoutFlowThread(&renderer) : m_next->flowThread();
+    if (renderer.isLayoutFlowThread())
+        m_flowThread = toLayoutFlowThread(&renderer);
+    else if (!renderer.isOutOfFlowPositioned() && !renderer.isColumnSpanAll())
+        m_flowThread = m_next->flowThread();
+    else
+        m_flowThread = nullptr;
     renderer.view()->pushLayoutState(*this);
     bool fixed = renderer.isOutOfFlowPositioned() && renderer.style()->position() == FixedPosition;
     if (fixed) {
         // FIXME: This doesn't work correctly with transforms.
         FloatPoint fixedOffset = renderer.view()->localToAbsolute(FloatPoint(), IsFixed);
         m_layoutOffset = LayoutSize(fixedOffset.x(), fixedOffset.y()) + offset;
     } else {
         m_layoutOffset = m_next->m_layoutOffset + offset;
     }
 
@@ skipping 79 matching lines @@
 }
 
 void LayoutState::addForcedColumnBreak(const LayoutBox& child, const LayoutUnit& childLogicalOffset)
 {
     if (!m_columnInfo || m_columnInfo->columnHeight())
         return;
     m_columnInfo->addForcedBreak(pageLogicalOffset(child, childLogicalOffset));
 }
 
 } // namespace blink