[New Multicolumn] Temporarily changing height is scary and can easily be avoided.

Source/core/rendering/RenderBlockFlow.cpp

 /*
  * 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
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 181 matching lines @@
     if (RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
         if (flowThread->computeColumnCountAndWidth())
             return true;
     }
     return relayoutChildren;
 }
 
 void RenderBlockFlow::checkForPaginationLogicalHeightChange(LayoutUnit& pageLogicalHeight, bool& pageLogicalHeightChanged, bool& hasSpecifiedPageLogicalHeight)
 {
     if (RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
-        updateLogicalHeight();
-        pageLogicalHeightChanged = contentLogicalHeight() != flowThread->columnHeightAvailable();
-        flowThread->setColumnHeightAvailable(std::max<LayoutUnit>(contentLogicalHeight(), 0));
-        setLogicalHeight(0);
+        LogicalExtentComputedValues computedValues;
+        computeLogicalHeight(LayoutUnit(), logicalTop(), computedValues);
+        LayoutUnit columnHeight = computedValues.m_extent - borderAndPaddingLogicalHeight() - scrollbarLogicalHeight();
+        pageLogicalHeightChanged = columnHeight != flowThread->columnHeightAvailable();
+        flowThread->setColumnHeightAvailable(std::max<LayoutUnit>(columnHeight, 0));
     } else if (hasColumns()) {
         ColumnInfo* colInfo = columnInfo();
 
         if (!pageLogicalHeight) {
             LayoutUnit oldLogicalHeight = logicalHeight();
             setLogicalHeight(0);
             // We need to go ahead and set our explicit page height if one exists, so that we can
             // avoid doing two layout passes.
             updateLogicalHeight();
             LayoutUnit columnHeight = contentLogicalHeight();
@@ skipping 2587 matching lines @@
 RenderBlockFlow::RenderBlockFlowRareData& RenderBlockFlow::ensureRareData()
 {
     if (m_rareData)
         return *m_rareData;
 
     m_rareData = adoptPtr(new RenderBlockFlowRareData(this));
     return *m_rareData;
 }
 
 } // namespace WebCore