Keeping track of descendants that draw content instead of recalcualting

cc/layers/tiled_layer.h

 // Copyright 2011 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_TILED_LAYER_H_
 #define CC_LAYERS_TILED_LAYER_H_
 
 #include "cc/base/cc_export.h"
 #include "cc/layers/contents_scaling_layer.h"
 #include "cc/resources/layer_tiling_data.h"
 #include "cc/resources/resource_format.h"
 
 namespace cc {
 class LayerUpdater;
 class PrioritizedResourceManager;
 class PrioritizedResource;
 class UpdatableTile;
 
 class CC_EXPORT TiledLayer : public ContentsScalingLayer {
  public:
   enum TilingOption {
     ALWAYS_TILE,
     NEVER_TILE,
     AUTO_TILE,
   };
 
   // Layer implementation.
   virtual void SetIsMask(bool is_mask) OVERRIDE;
   virtual void PushPropertiesTo(LayerImpl* layer) OVERRIDE;
-  virtual bool DrawsContent() const OVERRIDE;
   virtual void ReduceMemoryUsage() OVERRIDE;
   virtual void SetNeedsDisplayRect(const gfx::RectF& dirty_rect) OVERRIDE;
   virtual void SetLayerTreeHost(LayerTreeHost* layer_tree_host) OVERRIDE;
   virtual void SetTexturePriorities(const PriorityCalculator& priority_calc)
       OVERRIDE;
   virtual Region VisibleContentOpaqueRegion() const OVERRIDE;
   virtual bool Update(ResourceUpdateQueue* queue,
                       const OcclusionTracker<Layer>* occlusion) OVERRIDE;
   virtual void OnOutputSurfaceCreated() OVERRIDE;
 
@@ skipping 20 matching lines @@
 
   // Reset state on tiles that will be used for updating the layer.
   void ResetUpdateState();
 
   // After preparing an update, returns true if more painting is needed.
   bool NeedsIdlePaint();
   gfx::Rect IdlePaintRect();
 
   bool SkipsDraw() const { return skips_draw_; }
 
+  virtual bool HasDrawableContent() const OVERRIDE;
+
   // Virtual for testing
   virtual PrioritizedResourceManager* ResourceManager();
   const LayerTilingData* TilerForTesting() const { return tiler_.get(); }
   const PrioritizedResource* ResourceAtForTesting(int i, int j) const;
 
  private:
   virtual scoped_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl)
       OVERRIDE;
 
   void CreateTilerIfNeeded();
@@ skipping 57 matching lines @@
 
   TilingOption tiling_option_;
   scoped_ptr<LayerTilingData> tiler_;
 
   DISALLOW_COPY_AND_ASSIGN(TiledLayer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_TILED_LAYER_H_