When balancing columns, we must check inner multicols for unbreakable content.

third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MultiColumnFragmentainerGroup_h
 #define MultiColumnFragmentainerGroup_h
 
 #include "core/layout/LayoutMultiColumnFlowThread.h"
 #include "wtf/Allocator.h"
 
@@ skipping 66 matching lines @@
     unsigned columnIndexAtOffset(LayoutUnit offsetInFlowThread, ColumnIndexCalculationMode = ClampToExistingColumns) const;
 
     // The "CSS actual" value of column-count. This includes overflowing columns, if any.
     unsigned actualColumnCount() const;
 
 private:
     LayoutUnit heightAdjustedForRowOffset(LayoutUnit height) const;
     LayoutUnit calculateMaxColumnHeight() const;
     void setAndConstrainColumnHeight(LayoutUnit);
 
-    LayoutUnit calculateColumnHeight(BalancedColumnHeightCalculation) const;
+    LayoutUnit rebalanceColumnHeightIfNeeded() const;
 
     LayoutRect columnRectAt(unsigned columnIndex) const;
     LayoutUnit logicalTopInFlowThreadAt(unsigned columnIndex) const { return m_logicalTopInFlowThread + columnIndex * m_columnHeight; }
     LayoutRect flowThreadPortionRectAt(unsigned columnIndex) const;
     LayoutRect flowThreadPortionOverflowRectAt(unsigned columnIndex) const;
 
     // Return the column that the specified visual point belongs to. Only the coordinate on the
     // column progression axis is relevant. Every point belongs to a column, even if said point is
     // not inside any of the columns.
     unsigned columnIndexAtVisualPoint(const LayoutPoint& visualPoint) const;
@@ skipping 53 matching lines @@
 
 private:
     LayoutMultiColumnSet& m_columnSet;
 
     Vector<MultiColumnFragmentainerGroup, 1> m_groups;
 };
 
 } // namespace blink
 
 #endif // MultiColumnFragmentainerGroup_h