Need to roll back the multicol machinery state when re-laying out a block child.

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 245 matching lines @@
     void willBeRemovedFromTree() override;
     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 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;
 
     unsigned m_columnCount; // The used value of column-count
     LayoutUnit m_columnHeightAvailable; // Total height available to columns, or 0 if auto.
 
     // 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;
 
     bool m_columnHeightsChanged; // Set when column heights are out of sync with actual layout.
     bool m_progressionIsInline; // Always true for regular multicol. False for paged-y overflow.
     bool m_isBeingEvacuated;
 };
 
 // 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