The column balancer should ignore things outside the bounds of the row.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003-2013 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
@@ skipping 140 matching lines @@
 
     void removeFloatingObjectsFromDescendants();
     void markAllDescendantsWithFloatsForLayout(LayoutBox* floatToRemove = nullptr, bool inLayout = true);
     void markSiblingsWithFloatsForLayout(LayoutBox* floatToRemove = nullptr);
 
     bool containsFloats() const { return m_floatingObjects && !m_floatingObjects->set().isEmpty(); }
     bool containsFloat(LayoutBox*) const;
 
     void removeFloatingObjects();
 
+    LayoutBoxModelObject* virtualContinuation() const final { return continuation(); }
+    bool isAnonymousBlockContinuation() const { return continuation() && isAnonymousBlock(); }
+
+    using LayoutBoxModelObject::continuation;
+    using LayoutBoxModelObject::setContinuation;
+
     LayoutInline* inlineElementContinuation() const;
 
     void addChild(LayoutObject* newChild, LayoutObject* beforeChild = nullptr) override;
     void removeChild(LayoutObject*) override;
 
     void moveAllChildrenIncludingFloatsTo(LayoutBlock* toBlock, bool fullRemoveInsert);
 
     void childBecameFloatingOrOutOfFlow(LayoutBox* child);
     void collapseAnonymousBlockChild(LayoutBlockFlow* child);
 
@@ skipping 500 matching lines @@
 
 // END METHODS DEFINED IN LayoutBlockFlowLine
 
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutBlockFlow, isLayoutBlockFlow());
 
 } // namespace blink
 
 #endif // LayoutBlockFlow_h