It's not just the last column set that may need additional fragmentainer groups.

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 174 matching lines @@
     bool recalculateColumnHeights();
 
     void columnRuleStyleDidChange();
 
     // Remove the spanner placeholder and return true if the specified object is no longer a valid spanner.
     bool removeSpannerPlaceholderIfNoLongerValid(LayoutBox* spannerObjectInFlowThread);
 
     LayoutMultiColumnFlowThread* enclosingFlowThread() const;
     LayoutUnit blockOffsetInEnclosingFlowThread() const { ASSERT(enclosingFlowThread()); return m_blockOffsetInEnclosingFlowThread; }
 
-    // Return true if we have a fragmentainer group that can hold a column at the specified flow thread block offset.
-    bool hasFragmentainerGroupForColumnAt(LayoutUnit offsetInFlowThread) const;
-
     // If we've run out of columns in the last fragmentainer group (column row), we have to insert
     // another fragmentainer group in order to hold more columns. This means that we're moving to
     // the next outer column (in the enclosing fragmentation context).
     void appendNewFragmentainerGroupIfNeeded(LayoutUnit offsetInFlowThread);
 
     const char* name() const override { return "LayoutMultiColumnFlowThread"; }
 
 protected:
     LayoutMultiColumnFlowThread();
     void setProgressionIsInline(bool isInline) { m_progressionIsInline = isInline; }
@@ skipping 36 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