cc: Return resources to child compositor via a Callback.

cc/layers/delegated_renderer_layer.h

Index: cc/layers/delegated_renderer_layer.h
diff --git a/cc/layers/delegated_renderer_layer.h b/cc/layers/delegated_renderer_layer.h
index b3a078fba515702f71185646e19333ac3d8d279d..ab3bfd6314b0cbf139b84a9fa9ad8bd82154b241 100644
--- a/cc/layers/delegated_renderer_layer.h
+++ b/cc/layers/delegated_renderer_layer.h
@@ -5,6 +5,7 @@
 #ifndef CC_LAYERS_DELEGATED_RENDERER_LAYER_H_
 #define CC_LAYERS_DELEGATED_RENDERER_LAYER_H_
 
+#include "base/synchronization/lock.h"
 #include "cc/base/cc_export.h"
 #include "cc/layers/layer.h"
 #include "cc/resources/returned_resource.h"
@@ -42,17 +43,22 @@ class CC_EXPORT DelegatedRendererLayer : public Layer {
   virtual ~DelegatedRendererLayer();
 
  private:
+  void ReceiveUnusedResources(const ReturnedResourceArray& unused);
+
   scoped_ptr<DelegatedFrameData> frame_data_;
   gfx::RectF damage_in_frame_;
   gfx::Size frame_size_;
   gfx::Size display_size_;
-  ReturnedResourceArray unused_resources_for_child_compositor_;
 
   DelegatedRendererLayerClient* client_;
   bool needs_filter_context_;
 
+  base::Lock unused_resources_lock_;
+  ReturnedResourceArray unused_resources_for_child_compositor_;
+
   DISALLOW_COPY_AND_ASSIGN(DelegatedRendererLayer);
 };
 
 }  // namespace cc
+
 #endif  // CC_LAYERS_DELEGATED_RENDERER_LAYER_H_