Need to examine the *bottom* of fragmented content.

third_party/WebKit/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 69 matching lines @@
 
     void validateColumnSets();
     void invalidateColumnSets();
     bool hasValidColumnSetInfo() const { return !m_columnSetsInvalidated && !m_multiColumnSetList.isEmpty(); }
 
     void mapToVisibleRectInContainerSpace(const LayoutBoxModelObject* paintInvalidationContainer, LayoutRect&, const PaintInvalidationState*) const override;
 
     LayoutUnit pageLogicalHeightForOffset(LayoutUnit);
     LayoutUnit pageRemainingLogicalHeightForOffset(LayoutUnit, PageBoundaryRule);
 
-    virtual void contentWasLaidOut(LayoutUnit logicalTopInFlowThreadAfterPagination) = 0;
+    virtual void contentWasLaidOut(LayoutUnit logicalBottomInFlowThreadAfterPagination) = 0;
 
     // Find and return the next logical top after |flowThreadOffset| that can fit unbreakable
     // content as tall as |contentLogicalHeight|. |flowThreadOffset| is expected to be at the exact
     // top of a column that's known to not have enough space for |contentLogicalHeight|. This method
     // is called when the current column is too short to fit the content, in the hope that there
     // exists one that's tall enough further ahead. If no such column can be found,
     // |flowThreadOffset| will be returned.
     LayoutUnit nextLogicalTopForUnbreakableContent(LayoutUnit flowThreadOffset, LayoutUnit contentLogicalHeight) const;
 
     virtual bool isPageLogicalHeightKnown() const { return true; }
@@ skipping 54 matching lines @@
 // These structures are used by PODIntervalTree for debugging.
 #ifndef NDEBUG
 template <> struct ValueToString<LayoutMultiColumnSet*> {
     static String string(const LayoutMultiColumnSet* value) { return String::format("%p", value); }
 };
 #endif
 
 } // namespace blink
 
 #endif // LayoutFlowThread_h