[New Multicolumn] Preparatory work for nested multicol support.

Source/core/rendering/RenderMultiColumnFlowThread.h

 /*
  * 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
@@ skipping 16 matching lines @@
 #ifndef RenderMultiColumnFlowThread_h
 #define RenderMultiColumnFlowThread_h
 
 #include "core/rendering/RenderFlowThread.h"
 
 namespace blink {
 
 class RenderMultiColumnSet;
 class RenderMultiColumnSpannerPlaceholder;
 
+enum BalancedColumnHeightCalculation { GuessFromFlowThreadPortion, StretchBySpaceShortage };
+
 // Flow thread implementation for CSS multicol. This will be inserted as an anonymous child block of
 // the actual multicol container (i.e. the RenderBlockFlow whose style computes to non-auto
 // column-count and/or column-width). RenderMultiColumnFlowThread is the heart of the multicol
 // implementation, and there is only one instance per multicol container. Child content of the
 // multicol container is parented into the flow thread at the time of renderer insertion.
 //
 // Apart from this flow thread child, the multicol container will also have RenderMultiColumnSet
 // "region" children, which are used to position the columns visually. The flow thread is in charge
 // of layout, and, after having calculated the column width, it lays out content as if everything
 // were in one tall single column, except that there will typically be some amount of blank space
@@ skipping 161 matching lines @@
     LayoutUnit m_columnHeightAvailable; // Total height available to columns, or 0 if auto.
     bool m_inBalancingPass; // Set when relayouting for column balancing.
     bool m_needsColumnHeightsRecalculation; // Set when we need to recalculate the column set heights after layout.
     bool m_progressionIsInline; // Always true for regular multicol. False for paged-y overflow.
     bool m_isBeingEvacuated;
 };
 
 } // namespace blink
 
 #endif // RenderMultiColumnFlowThread_h