Keeping track of descendants that draw content instead of recalcualting

cc/layers/picture_layer.h

Index: cc/layers/picture_layer.h
diff --git a/cc/layers/picture_layer.h b/cc/layers/picture_layer.h
index 406ffad2f1785b5d3e4e7563f27299b63a26fe61..80bb4d867a6b01ff5c50a390fb835b0735a3a81a 100644
--- a/cc/layers/picture_layer.h
+++ b/cc/layers/picture_layer.h
@@ -21,10 +21,9 @@ class CC_EXPORT PictureLayer : public Layer {
  public:
   static scoped_refptr<PictureLayer> Create(ContentLayerClient* client);
 
-  void ClearClient() { client_ = NULL; }
+  void ClearClient();
 
   // Layer interface.
-  virtual bool DrawsContent() const OVERRIDE;
   virtual scoped_ptr<LayerImpl> CreateLayerImpl(
       LayerTreeImpl* tree_impl) OVERRIDE;
   virtual void SetLayerTreeHost(LayerTreeHost* host) OVERRIDE;
@@ -49,6 +48,7 @@ class CC_EXPORT PictureLayer : public Layer {
   explicit PictureLayer(ContentLayerClient* client);
   virtual ~PictureLayer();
 
+  virtual bool HasDrawableContent() const OVERRIDE;
   void UpdateCanUseLCDText();
 
  private: