Compute if a layer is drawn without LayerTree hierarchy

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index f573d8e30e93a5717e699197f1766832e27420d7..8aaed1b8b49278a32678df34c4ade2ae69664a5b 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -516,6 +516,10 @@ class COMPOSITOR_EXPORT Layer
 
   // A cached copy of |Compositor::device_scale_factor()|.
   float device_scale_factor_;
+  // When a layer become invisible, we make the corresponding cc_layer
+  // transparent (opacity = 0) and cache its actual opacity value. This is used
+  // to set it back when the layer becomes visible.
+  float cached_cc_layer_opacity_;
 
   // A cached copy of the nine patch layer's image and aperture.
   // These are required for device scale factor change.