[New Multicolumn] Correct paint rectangle calculation for compositing.

Source/core/rendering/compositing/RenderLayerCompositor.cpp

Index: Source/core/rendering/compositing/RenderLayerCompositor.cpp
diff --git a/Source/core/rendering/compositing/RenderLayerCompositor.cpp b/Source/core/rendering/compositing/RenderLayerCompositor.cpp
index b7d9c73d4bb3f519cd6f3f56d553d4244635a901..2ade68c74973e74b2db94f3dc026029fa308c3f0 100644
--- a/Source/core/rendering/compositing/RenderLayerCompositor.cpp
+++ b/Source/core/rendering/compositing/RenderLayerCompositor.cpp
@@ -756,9 +756,7 @@ void RenderLayerCompositor::setOverlayLayer(GraphicsLayer* layer)
 
 bool RenderLayerCompositor::canBeComposited(const RenderLayer* layer) const
 {
-    // FIXME: We disable accelerated compositing for elements in a RenderFlowThread as it doesn't work properly.
-    // See http://webkit.org/b/84900 to re-enable it.
-    return m_hasAcceleratedCompositing && layer->isSelfPaintingLayer() && !layer->subtreeIsInvisible() && layer->renderer()->flowThreadState() == RenderObject::NotInsideFlowThread;
+    return m_hasAcceleratedCompositing && layer->isSelfPaintingLayer() && !layer->subtreeIsInvisible();
 }
 
 // Return true if the given layer is a stacking context and has compositing child