Avoid stack overflow triggered by out-of-band layout of flexbox child.

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 46 matching lines @@
     bool supportsPaintInvalidationStateCachedOffsets() const override { return false; }
 
     static LayoutFlowThread* locateFlowThreadContainingBlockOf(const LayoutObject&);
 
     void layout() override;
 
     // Always create a Layer for the LayoutFlowThread so that we
     // can easily avoid drawing the children directly.
     DeprecatedPaintLayerType layerTypeRequired() const final { return NormalDeprecatedPaintLayer; }
 
-    // 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).
-    virtual void skipColumnSpanner(LayoutBox*, LayoutUnit logicalTopInFlowThread) { }
-
     virtual void flowThreadDescendantWasInserted(LayoutObject*) { }
     virtual void flowThreadDescendantWillBeRemoved(LayoutObject*) { }
     virtual void flowThreadDescendantStyleWillChange(LayoutObject*, StyleDifference, const ComputedStyle& newStyle) { }
     virtual void flowThreadDescendantStyleDidChange(LayoutObject*, StyleDifference, const ComputedStyle& oldStyle) { }
 
     bool nodeAtPoint(HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction) final;
 
     virtual void addColumnSetToThread(LayoutMultiColumnSet*) = 0;
     virtual void removeColumnSetFromThread(LayoutMultiColumnSet*);
 
@@ skipping 77 matching lines @@
 };
 
 template <> struct ValueToString<LayoutMultiColumnSet*> {
     static String string(const LayoutMultiColumnSet* value) { return String::format("%p", value); }
 };
 #endif
 
 } // namespace blink
 
 #endif // LayoutFlowThread_h