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

third_party/WebKit/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
@@ skipping 321 matching lines @@
 
     MultiColumnSetSearchAdapter adapter(offset);
     m_multiColumnSetIntervalTree.allOverlapsWithAdapter<MultiColumnSetSearchAdapter>(adapter);
 
     // If no set was found, the offset is in the flow thread overflow.
     if (!adapter.result() && !m_multiColumnSetList.isEmpty())
         return m_multiColumnSetList.last();
     return adapter.result();
 }
 
-void LayoutMultiColumnFlowThread::layoutColumns(bool relayoutChildren, SubtreeLayoutScope& layoutScope)
+void LayoutMultiColumnFlowThread::layoutColumns(SubtreeLayoutScope& layoutScope)
 {
-    if (relayoutChildren)
-        layoutScope.setChildNeedsLayout(this);
+    // Since we ended up here, it means that the multicol container (our parent) needed
+    // layout. Since contents of the multicol container are diverted to the flow thread, the flow
+    // thread needs layout as well.
+    layoutScope.setChildNeedsLayout(this);
 
     m_needsColumnHeightsRecalculation = false;
-    if (!needsLayout()) {
-        // Just before the multicol container (our parent LayoutBlockFlow) finishes laying out, it
-        // will call recalculateColumnHeights() on us unconditionally, but we only want that method
-        // to do any work if we actually laid out the flow thread. Otherwise, the balancing
-        // machinery would kick in needlessly, and trigger additional layout passes. Furthermore, we
-        // actually depend on a proper flowthread layout pass in order to do balancing, since it's
-        // flowthread layout that sets up content runs.
-        return;
-    }
 
     m_blockOffsetInEnclosingFlowThread = enclosingFlowThread() ? multiColumnBlockFlow()->offsetFromLogicalTopOfFirstPage() : LayoutUnit();
 
     for (LayoutBox* columnBox = firstMultiColumnBox(); columnBox; columnBox = columnBox->nextSiblingMultiColumnBox()) {
         if (!columnBox->isLayoutMultiColumnSet()) {
             ASSERT(columnBox->isLayoutMultiColumnSpannerPlaceholder()); // no other type is expected.
             m_needsColumnHeightsRecalculation = true;
             continue;
         }
         LayoutMultiColumnSet* columnSet = toLayoutMultiColumnSet(columnBox);
@@ skipping 568 matching lines @@
     appendNewFragmentainerGroupIfNeeded(logicalTopInFlowThreadAfterPagination);
 }
 
 void LayoutMultiColumnFlowThread::updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight)
 {
     if (LayoutMultiColumnSet* multicolSet = columnSetAtBlockOffset(offset))
         multicolSet->updateMinimumColumnHeight(offset, minHeight);
 }
 
 }