Add a runtime flag for the column-fill property.

Source/core/layout/LayoutMultiColumnSet.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
@@ skipping 12 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "core/layout/LayoutMultiColumnSet.h"
 
 #include "core/editing/PositionWithAffinity.h"
 #include "core/layout/LayoutMultiColumnFlowThread.h"
 #include "core/layout/MultiColumnFragmentainerGroup.h"
 #include "core/paint/MultiColumnSetPainter.h"
+#include "platform/RuntimeEnabledFeatures.h"
 
 namespace blink {
 
 LayoutMultiColumnSet::LayoutMultiColumnSet(LayoutFlowThread* flowThread)
     : LayoutBlockFlow(0)
     , m_fragmentainerGroups(*this)
     , m_flowThread(flowThread)
 {
 }
 
@@ skipping 87 matching lines @@
         clipRect = LayoutRect(minX, minY, maxX - minX, maxY - minY);
     }
 
     return clipRect;
 }
 
 bool LayoutMultiColumnSet::heightIsAuto() const
 {
     LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread();
     if (!flowThread->isLayoutPagedFlowThread()) {
-        if (multiColumnBlockFlow()->style()->columnFill() == ColumnFillBalance)
-            return true;
+        if (RuntimeEnabledFeatures::unprefixMulticolEnabled()) {

[Julien - ping for review, 2015/05/22 22:09:18]

Comment about why we do that and what the behavior is, por favor! The comment
from the previous iteration was great.

[mstensho (USE GERRIT), 2015/05/25 18:47:20]

Done.

+            if (multiColumnBlockFlow()->style()->columnFill() == ColumnFillBalance)
+                return true;
+        }
         if (LayoutBox* next = nextSiblingBox()) {
             if (next->isLayoutMultiColumnSpannerPlaceholder()) {
                 // If we're followed by a spanner, we need to balance.
                 return true;
             }
         }
     }
     return !flowThread->columnHeightAvailable();
 }
 
@@ skipping 165 matching lines @@
 
 LayoutRect LayoutMultiColumnSet::flowThreadPortionRect() const
 {
     LayoutRect portionRect(LayoutUnit(), logicalTopInFlowThread(), pageLogicalWidth(), logicalHeightInFlowThread());
     if (!isHorizontalWritingMode())
         return portionRect.transposedRect();
     return portionRect;
 }
 
 }