Compute if a layer is drawn without LayerTree hierarchy

ui/compositor/layer.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_COMPOSITOR_LAYER_H_
 #define UI_COMPOSITOR_LAYER_H_
 
 #include <stddef.h>
 
 #include <string>
@@ skipping 496 matching lines @@
   scoped_refptr<cc::Layer> content_layer_;
   scoped_refptr<cc::NinePatchLayer> nine_patch_layer_;
   scoped_refptr<cc::TextureLayer> texture_layer_;
   scoped_refptr<cc::SolidColorLayer> solid_color_layer_;
   scoped_refptr<cc::DelegatedRendererLayer> delegated_renderer_layer_;
   scoped_refptr<cc::SurfaceLayer> surface_layer_;
   cc::Layer* cc_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.
   gfx::ImageSkia nine_patch_layer_image_;
   gfx::Rect nine_patch_layer_aperture_;
 
   // The mailbox used by texture_layer_.
   cc::TextureMailbox mailbox_;
 
   // The callback to release the mailbox. This is only set after
   // SetTextureMailbox is called, before we give it to the TextureLayer.
   scoped_ptr<cc::SingleReleaseCallback> mailbox_release_callback_;
 
   // The size of the frame or texture in DIP, set when SetShowDelegatedContent
   // or SetTextureMailbox was called.
   gfx::Size frame_size_in_dip_;
 
   DISALLOW_COPY_AND_ASSIGN(Layer);
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_LAYER_H_