[New Multicolumn] Never composite flow threads.

Source/core/layout/compositing/DeprecatedPaintLayerCompositor.cpp

 /*
  * Copyright (C) 2009, 2010 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 734 matching lines @@
     layer->setPotentialCompositingReasonsFromStyle(m_compositingReasonFinder.potentialCompositingReasonsFromStyle(layer->layoutObject()));
 }
 
 void DeprecatedPaintLayerCompositor::updateDirectCompositingReasons(DeprecatedPaintLayer* layer)
 {
     layer->setCompositingReasons(m_compositingReasonFinder.directReasons(layer), CompositingReasonComboAllDirectReasons);
 }
 
 bool DeprecatedPaintLayerCompositor::canBeComposited(const DeprecatedPaintLayer* layer) const
 {
-    return m_hasAcceleratedCompositing && layer->isSelfPaintingLayer() && !layer->subtreeIsInvisible();
+    return m_hasAcceleratedCompositing && layer->isSelfPaintingLayer() && !layer->subtreeIsInvisible() && !layer->layoutObject()->isLayoutFlowThread();
 }
 
 // Return true if the given layer is a stacking context and has compositing child
 // layers that it needs to clip. In this case we insert a clipping GraphicsLayer
 // into the hierarchy between this layer and its children in the z-order hierarchy.
 bool DeprecatedPaintLayerCompositor::clipsCompositingDescendants(const DeprecatedPaintLayer* layer) const
 {
     return layer->hasCompositingDescendant() && layer->layoutObject()->hasClipOrOverflowClip();
 }
 
@@ skipping 413 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "LocalFrame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink