cc: Async readback.

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index 19aa727ffe3e38d3bb6b09223fb3ab936ad6801a..f53572ed938898a45732cc1a28b1981714fe093d 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -75,6 +75,14 @@ class CC_EXPORT LayerImpl : LayerAnimationValueObserver {
   // Warning: This does not preserve tree structure invariants.
   void ClearChildList();
 
+  void PassRequestCopyCallbacks(
+      std::vector<RenderPass::RequestCopyAsBitmapCallback>* callbacks);
+  void TakeRequestCopyCallbacks(
+      std::vector<RenderPass::RequestCopyAsBitmapCallback>* callbacks);
+  bool HasRequestCopyCallback() const {
+    return !request_copy_callbacks_.empty();
+  }
+
   void SetMaskLayer(scoped_ptr<LayerImpl> mask_layer);
   LayerImpl* mask_layer() { return mask_layer_.get(); }
   const LayerImpl* mask_layer() const { return mask_layer_.get(); }
@@ -529,6 +537,8 @@ class CC_EXPORT LayerImpl : LayerAnimationValueObserver {
   ScrollbarLayerImpl* horizontal_scrollbar_layer_;
   ScrollbarLayerImpl* vertical_scrollbar_layer_;
 
+  std::vector<RenderPass::RequestCopyAsBitmapCallback> request_copy_callbacks_;
+
   // Group of properties that need to be computed based on the layer tree
   // hierarchy before layers can be drawn.
   DrawProperties<LayerImpl, RenderSurfaceImpl> draw_properties_;