[New Multicolumn] Never composite flow threads.

Source/core/layout/compositing/DeprecatedPaintLayerCompositor.cpp

Index: Source/core/layout/compositing/DeprecatedPaintLayerCompositor.cpp
diff --git a/Source/core/layout/compositing/DeprecatedPaintLayerCompositor.cpp b/Source/core/layout/compositing/DeprecatedPaintLayerCompositor.cpp
index 161397536820bf71b96f3fadfc357c10d88e3e73..bdf191204e09aec150776e11968d329aa3f5f2af 100644
--- a/Source/core/layout/compositing/DeprecatedPaintLayerCompositor.cpp
+++ b/Source/core/layout/compositing/DeprecatedPaintLayerCompositor.cpp
@@ -752,7 +752,7 @@ void DeprecatedPaintLayerCompositor::updateDirectCompositingReasons(DeprecatedPa
 
 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