Invalidate column rules when the width of a multicol container changes.

third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.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 130 matching lines @@
     // Layout of flow thread content that's to be rendered inside this column set begins. This
     // happens at the beginning of flow thread layout, and when advancing from a previous column set
     // or spanner to this one.
     void beginFlow(LayoutUnit offsetInFlowThread);
 
     // Layout of flow thread content that was to be rendered inside this column set has
     // finished. This happens at end of flow thread layout, and when advancing to the next column
     // set or spanner.
     void endFlow(LayoutUnit offsetInFlowThread);
 
+    void styleDidChange(StyleDifference, const ComputedStyle* oldStyle) override;
     void layout() override;
 
     void computeIntrinsicLogicalWidths(LayoutUnit& minLogicalWidth, LayoutUnit& maxLogicalWidth) const final;
 
     void attachToFlowThread();
     void detachFromFlowThread();
 
     // The top of the page nearest to the specified block offset. All in flowthread coordinates.
     LayoutUnit pageLogicalTopForOffset(LayoutUnit offset) const;
 
@@ skipping 42 matching lines @@
 
     bool m_initialHeightCalculated;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutMultiColumnSet, isLayoutMultiColumnSet());
 
 } // namespace blink
 
 #endif // LayoutMultiColumnSet_h