Changing out-of-flow-ness on a multicol child may affect the need for column sets.

Source/core/layout/LayoutMultiColumnFlowThread.cpp

 /*
  * 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
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         // If there were no adjacent spanners, it has to mean that there's only one column set,
         // since it's only spanners that may cause creation of multiple sets.
         columnSetToRemove = firstMultiColumnSet();
         ASSERT(columnSetToRemove);
         ASSERT(!columnSetToRemove->nextSiblingMultiColumnSet());
     }
     ASSERT(columnSetToRemove);
     columnSetToRemove->destroy();
 }
 
+void LayoutMultiColumnFlowThread::flowThreadDescendantStyleWillChange(LayoutObject* descendant, StyleDifference diff, const ComputedStyle& newStyle)
+{
+    // If an in-flow descendant goes out-of-flow, we may have to remove a column set.
+    if (newStyle.hasOutOfFlowPosition() && !styleRef().hasOutOfFlowPosition())
+        flowThreadDescendantWillBeRemoved(descendant);
+}
+
+void LayoutMultiColumnFlowThread::flowThreadDescendantStyleDidChange(LayoutObject* descendant, StyleDifference diff, const ComputedStyle& oldStyle)
+{
+    // If an out-of-flow descendant goes in-flow, we may have to insert a column set.
+    if (oldStyle.hasOutOfFlowPosition() && !styleRef().hasOutOfFlowPosition())
+        flowThreadDescendantWasInserted(descendant);
+}
+
 void LayoutMultiColumnFlowThread::computePreferredLogicalWidths()
 {
     LayoutFlowThread::computePreferredLogicalWidths();
 
     // The min/max intrinsic widths calculated really tell how much space elements need when
     // laid out inside the columns. In order to eventually end up with the desired column width,
     // we need to convert them to values pertaining to the multicol container.
     const LayoutBlockFlow* multicolContainer = multiColumnBlockFlow();
     const ComputedStyle* multicolStyle = multicolContainer->style();
     int columnCount = multicolStyle->hasAutoColumnCount() ? 1 : multicolStyle->columnCount();
@@ skipping 75 matching lines @@
 }
 
 bool LayoutMultiColumnFlowThread::isPageLogicalHeightKnown() const
 {
     if (LayoutMultiColumnSet* columnSet = lastMultiColumnSet())
         return columnSet->pageLogicalHeight();
     return false;
 }
 
 }