Always lay out the flow thread when the multicol container is laid out.

third_party/WebKit/Source/core/layout/LayoutBlockFlow.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 160 matching lines @@
     layoutBlockFlow->setDocumentForAnonymous(document);
     return layoutBlockFlow;
 }
 
 LayoutObject* LayoutBlockFlow::layoutSpecialExcludedChild(bool relayoutChildren, SubtreeLayoutScope& layoutScope)
 {
     LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread();
     if (!flowThread)
         return nullptr;
     setLogicalTopForChild(*flowThread, borderBefore() + paddingBefore());
-    flowThread->layoutColumns(relayoutChildren, layoutScope);
+    flowThread->layoutColumns(layoutScope);
     determineLogicalLeftPositionForChild(*flowThread);
     return flowThread;
 }
 
 bool LayoutBlockFlow::updateLogicalWidthAndColumnWidth()
 {
     bool relayoutChildren = LayoutBlock::updateLogicalWidthAndColumnWidth();
     if (LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
         if (flowThread->needsNewWidth())
             return true;
@@ skipping 2851 matching lines @@
     FrameView* frameView = document().view();
     LayoutUnit top = (style()->position() == FixedPosition) ? 0 : frameView->scrollOffset().height();
     int visibleHeight = frameView->visibleContentRect(IncludeScrollbars).height();
     if (size().height() < visibleHeight)
         top += (visibleHeight - size().height()) / 2;
     setY(top);
     dialog->setCentered(top);
 }
 
 } // namespace blink