Descendants may become or cease to be spanners when an ancestor changes style.

third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.h

 /*
  * Copyright (C) 2012 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 292 matching lines @@
   void flowThreadDescendantWasInserted(LayoutObject*) final;
   void flowThreadDescendantWillBeRemoved(LayoutObject*) final;
   void flowThreadDescendantStyleWillChange(
       LayoutBox*,
       StyleDifference,
       const ComputedStyle& newStyle) override;
   void flowThreadDescendantStyleDidChange(
       LayoutBox*,
       StyleDifference,
       const ComputedStyle& oldStyle) override;
+  void toggleSpannersInSubtree(LayoutBox*);
   void computePreferredLogicalWidths() override;
   void computeLogicalHeight(LayoutUnit logicalHeight,
                             LayoutUnit logicalTop,
                             LogicalExtentComputedValues&) const override;
   void updateLogicalWidth() override;
   void contentWasLaidOut(
       LayoutUnit logicalBottomInFlowThreadAfterPagination) override;
   bool canSkipLayout(const LayoutBox&) const override;
   MultiColumnLayoutState multiColumnLayoutState() const override;
   void restoreMultiColumnLayoutState(const MultiColumnLayoutState&) override;
 
   // The last set we worked on. It's not to be used as the "current set". The
   // concept of a "current set" is difficult, since layout may jump back and
   // forth in the tree, due to wrong top location estimates (due to e.g. margin
   // collapsing), and possibly for other reasons.
   LayoutMultiColumnSet* m_lastSetWorkedOn;
 
+#if DCHECK_IS_ON()
+  // Used to check consistency between calls to
+  // flowThreadDescendantStyleWillChange() and
+  // flowThreadDescendantStyleDidChange().
+  static const LayoutBox* s_styleChangedBox;
+#endif
+
   // The used value of column-count
   unsigned m_columnCount;
   // Total height available to columns, or 0 if auto.
   LayoutUnit m_columnHeightAvailable;
 
   // Cached block offset from this flow thread to the enclosing fragmentation
   // context, if any. In
   // the coordinate space of the enclosing fragmentation context.
   LayoutUnit m_blockOffsetInEnclosingFragmentationContext;
 
   // Set when column heights are out of sync with actual layout.
   bool m_columnHeightsChanged;
+
   // Always true for regular multicol. False for paged-y overflow.
   bool m_progressionIsInline;
+
   bool m_isBeingEvacuated;
+
+  // Specifies whether the the descendant whose style is about to change could
+  // contain spanners or not. The flag is set in
+  // flowThreadDescendantStyleWillChange(), and then checked in
+  // flowThreadDescendantStyleDidChange().
+  static bool s_couldContainSpanners;
+
+  static bool s_toggleSpannersIfNeeded;
 };
 
 // Cannot use DEFINE_LAYOUT_OBJECT_TYPE_CASTS here, because
 // isMultiColumnFlowThread() is defined in LayoutFlowThread, not in
 // LayoutObject.
 DEFINE_TYPE_CASTS(LayoutMultiColumnFlowThread,
                   LayoutFlowThread,
                   object,
                   object->isLayoutMultiColumnFlowThread(),
                   object.isLayoutMultiColumnFlowThread());
 
 }  // namespace blink
 
 #endif  // LayoutMultiColumnFlowThread_h