Changing out-of-flow-ness on a multicol child may affect the need for column sets.

Source/core/layout/LayoutFlowThread.h

 /*
  * Copyright (C) 2011 Adobe Systems Incorporated. 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.
@@ skipping 53 matching lines @@
 
     // Skip past a column spanner during flow thread layout. Spanners are not laid out inside the
     // flow thread, since the flow thread is not in a spanner's containing block chain (since the
     // containing block is the multicol container). If the spanner follows right after a column set
     // (as opposed to following another spanner), we may have to stretch the flow thread to ensure
     // completely filled columns in the preceding column set. Return this adjustment, if any.
     virtual LayoutUnit skipColumnSpanner(LayoutBox*, LayoutUnit logicalTopInFlowThread) { return LayoutUnit(); }
 
     virtual void flowThreadDescendantWasInserted(LayoutObject*) { }
     virtual void flowThreadDescendantWillBeRemoved(LayoutObject*) { }
+    virtual void flowThreadDescendantStyleWillChange(LayoutObject*, StyleDifference, const ComputedStyle& newStyle) { }
+    virtual void flowThreadDescendantStyleDidChange(LayoutObject*, StyleDifference, const ComputedStyle& oldStyle) { }
 
     virtual bool nodeAtPoint(HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction) override final;
 
     virtual void addColumnSetToThread(LayoutMultiColumnSet*) = 0;
     virtual void removeColumnSetFromThread(LayoutMultiColumnSet*);
 
     virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const override;
 
     bool hasColumnSets() const { return m_multiColumnSetList.size(); }
 
@@ skipping 79 matching lines @@
 };
 
 template <> struct ValueToString<LayoutMultiColumnSet*> {
     static String string(const LayoutMultiColumnSet* value) { return String::format("%p", value); }
 };
 #endif
 
 } // namespace blink
 
 #endif // LayoutFlowThread_h