[New Multicolumn] Don't return the wrong flow thread from locateFlowThreadContainingBlock().

Source/core/layout/LayoutState.h

 /*
  * 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 57 matching lines @@
     LayoutUnit pageLogicalHeight() const { return m_pageLogicalHeight; }
     bool pageLogicalHeightChanged() const { return m_pageLogicalHeightChanged; }
     bool containingBlockLogicalWidthChanged() const { return m_containingBlockLogicalWidthChanged; }
 
     LayoutState* next() const { return m_next; }
 
     bool needsBlockDirectionLocationSetBeforeLayout() const { return m_isPaginated && m_pageLogicalHeight; }
 
     LayoutFlowThread* flowThread() const { return m_flowThread; }
 
+    // Used to temporarily set m_flowThread to nullptr. Needed because of crbug.com/370461 (list item markers).
+    void setFlowThread(LayoutFlowThread* flowThread) { m_flowThread = flowThread; }
+
     ColumnInfo* columnInfo() const { return m_columnInfo; }
 
     LayoutObject& layoutObject() const { return m_renderer; }
 
 private:
     friend class ForceHorriblySlowRectMapping;
 
     // Do not add anything apart from bitfields until after m_columnInfo. See https://bugs.webkit.org/show_bug.cgi?id=100173
     bool m_isPaginated : 1;
     // If our page height has changed, this will force all blocks to relayout.
@@ skipping 13 matching lines @@
     LayoutUnit m_pageLogicalHeight;
     // The offset of the start of the first page in the nearest enclosing pagination model.
     LayoutSize m_pageOffset;
 
     LayoutObject& m_renderer;
 };
 
 } // namespace blink
 
 #endif // LayoutState_h