Keeping track of descendants that draw content instead of recalcualting

cc/layers/content_layer.h

 // Copyright 2010 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 CC_LAYERS_CONTENT_LAYER_H_
 #define CC_LAYERS_CONTENT_LAYER_H_
 
 #include "base/basictypes.h"
 #include "cc/base/cc_export.h"
 #include "cc/layers/tiled_layer.h"
@@ skipping 20 matching lines @@
   ContentLayerClient* client_;
 
   DISALLOW_COPY_AND_ASSIGN(ContentLayerPainter);
 };
 
 // A layer that renders its contents into an SkCanvas.
 class CC_EXPORT ContentLayer : public TiledLayer {
  public:
   static scoped_refptr<ContentLayer> Create(ContentLayerClient* client);
 
-  void ClearClient() { client_ = NULL; }
+  void ClearClient();
 
-  virtual bool DrawsContent() const OVERRIDE;
   virtual void SetLayerTreeHost(LayerTreeHost* layer_tree_host) OVERRIDE;
   virtual void SetTexturePriorities(const PriorityCalculator& priority_calc)
       OVERRIDE;
   virtual bool Update(ResourceUpdateQueue* queue,
                       const OcclusionTracker<Layer>* occlusion) OVERRIDE;
   virtual bool NeedMoreUpdates() OVERRIDE;
 
   virtual void SetContentsOpaque(bool contents_opaque) OVERRIDE;
 
   virtual bool SupportsLCDText() const OVERRIDE;
 
   virtual skia::RefPtr<SkPicture> GetPicture() const OVERRIDE;
 
   virtual void OnOutputSurfaceCreated() OVERRIDE;
 
  protected:
   explicit ContentLayer(ContentLayerClient* client);
   virtual ~ContentLayer();
 
+  virtual bool HasDrawableContent() const OVERRIDE;
+
   // TiledLayer implementation.
   virtual LayerUpdater* Updater() const OVERRIDE;
 
  private:
   // TiledLayer implementation.
   virtual void CreateUpdaterIfNeeded() OVERRIDE;
 
   void UpdateCanUseLCDText();
 
   ContentLayerClient* client_;
   scoped_refptr<ContentLayerUpdater> updater_;
   bool can_use_lcd_text_last_frame_;
 
   DISALLOW_COPY_AND_ASSIGN(ContentLayer);
 };
 
 }  // namespace cc
 #endif  // CC_LAYERS_CONTENT_LAYER_H_