Backout d4985245dfd55ba44e0417c42c956e03d094b0df (bug 1136766) for talos regression

--HG--
extra : commitid : FLbaQb0zd8o
extra : rebase_source : 2d1a6691cadd24d46da7b65971bcd0818b1f75f6

gfx/layers/composite/LayerManagerComposite.cpp

@@ -226,11 +226,7 @@ LayerManagerComposite::ApplyOcclusionCulling(Layer* aLayer, nsIntRegion& aOpaque
   LayerComposite *composite = aLayer->AsLayerComposite();
   if (!localOpaque.IsEmpty()) {
     nsIntRegion visible = composite->GetShadowVisibleRegion();
-    nsIntRegion afterCulling;
-    afterCulling.Sub(visible, localOpaque);
-    // Intersect the original region with the bounds of the culled region so
-    // that we don't increase the region's complexity.
-    visible.AndWith(afterCulling.GetBounds());
+    visible.Sub(visible, localOpaque);
     composite->SetShadowVisibleRegion(visible);
   }