Update outer flow thread membership before changing multicolness.

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 200 matching lines @@
     void createAndInsertMultiColumnSet(LayoutBox* insertBefore = nullptr);
     void createAndInsertSpannerPlaceholder(LayoutBox* spannerObjectInFlowThread, LayoutObject* insertedBeforeInFlowThread);
     void destroySpannerPlaceholder(LayoutMultiColumnSpannerPlaceholder*);
     virtual bool descendantIsValidColumnSpanner(LayoutObject* descendant) const;
 
     void addColumnSetToThread(LayoutMultiColumnSet*) override;
     void willBeRemovedFromTree() override;
     void skipColumnSpanner(LayoutBox*, LayoutUnit logicalTopInFlowThread) override;
     void flowThreadDescendantWasInserted(LayoutObject*) final;
     void flowThreadDescendantWillBeRemoved(LayoutObject*) final;
-    void flowThreadDescendantStyleWillChange(LayoutObject*, StyleDifference, const ComputedStyle& newStyle) override;
-    void flowThreadDescendantStyleDidChange(LayoutObject*, StyleDifference, const ComputedStyle& oldStyle) override;
+    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 setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage) override;
     void updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight) override;
     bool addForcedColumnBreak(LayoutUnit, LayoutObject* breakChild, bool isBefore, LayoutUnit* offsetBreakAdjustment = nullptr) 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.
@@ skipping 12 matching lines @@
     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