Keeping track of descendants that draw content instead of recalcualting

cc/layers/image_layer.h

Index: cc/layers/image_layer.h
diff --git a/cc/layers/image_layer.h b/cc/layers/image_layer.h
index 2f3255f092af7f3cd55556b82214f2a359b30bae..158cc4fc34c2629e7eb6fb42d213c2a450f08834 100644
--- a/cc/layers/image_layer.h
+++ b/cc/layers/image_layer.h
@@ -19,7 +19,6 @@ class CC_EXPORT ImageLayer : public TiledLayer {
   static scoped_refptr<ImageLayer> Create();
 
   // Layer implementation.
-  virtual bool DrawsContent() const OVERRIDE;
   virtual void SetTexturePriorities(const PriorityCalculator& priority_calc)
       OVERRIDE;
   virtual bool Update(ResourceUpdateQueue* queue,
@@ -36,6 +35,9 @@ class CC_EXPORT ImageLayer : public TiledLayer {
 
   void SetBitmap(const SkBitmap& image);
 
+ protected:
+  virtual void UpdateDrawsContent(bool draws_content) OVERRIDE;
+
  private:
   ImageLayer();
   virtual ~ImageLayer();