Keeping track of descendants that draw content instead of recalcualting

cc/layers/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_LAYER_H_
 #define CC_LAYERS_LAYER_H_
 
 #include <set>
 #include <string>
 
@@ skipping 313 matching lines @@
 
   void set_use_parent_backface_visibility(bool use) {
     use_parent_backface_visibility_ = use;
   }
   bool use_parent_backface_visibility() const {
     return use_parent_backface_visibility_;
   }
 
   virtual void SetLayerTreeHost(LayerTreeHost* host);
 
-  bool HasDelegatedContent() const { return false; }
+  virtual bool HasDelegatedContent() const;
   bool HasContributingDelegatedRenderPasses() const { return false; }
 
   void SetIsDrawable(bool is_drawable);
 
   void SetHideLayerAndSubtree(bool hide);
   bool hide_layer_and_subtree() const { return hide_layer_and_subtree_; }
 
   void SetReplicaLayer(Layer* layer);
   Layer* replica_layer() { return replica_layer_.get(); }
   const Layer* replica_layer() const { return replica_layer_.get(); }
 
   bool has_mask() const { return !!mask_layer_.get(); }
   bool has_replica() const { return !!replica_layer_.get(); }
   bool replica_has_mask() const {
     return replica_layer_.get() &&
            (mask_layer_.get() || replica_layer_->mask_layer_.get());
   }
 
-  // These methods typically need to be overwritten by derived classes.
+  int NumDescendantsThatDrawContent() const;
+
+  // This is only virtual for tests.
+  // TODO(awoloszyn): Remove this once we no longer need it for tests
   virtual bool DrawsContent() const;
+
+  // This methods typically need to be overwritten by derived classes.
   virtual void SavePaintProperties();
   // Returns true iff any resources were updated that need to be committed.
   virtual bool Update(ResourceUpdateQueue* queue,
                       const OcclusionTracker<Layer>* occlusion);
   virtual bool NeedMoreUpdates();
   virtual void SetIsMask(bool is_mask) {}
   virtual void ReduceMemoryUsage() {}
   virtual void OnOutputSurfaceCreated() {}
   virtual bool IsSuitableForGpuRasterization() const;
 
@@ skipping 114 matching lines @@
   void SetNeedsCommit();
   // Called when there's been a change in layer structure.  Implies both
   // SetNeedsUpdate and SetNeedsCommit, but not SetNeedsPushProperties.
   void SetNeedsFullTreeSync();
 
   // Called when the next commit should wait until the pending tree is activated
   // before finishing the commit and unblocking the main thread. Used to ensure
   // unused resources on the impl thread are returned before commit completes.
   void SetNextCommitWaitsForActivation();
 
+  // Will recalculate whether the layer draws content and set draws_content_
+  // appropriately.
+  void UpdateDrawsContent(bool has_drawable_content);
+  virtual bool HasDrawableContent() const;
+
+  // Called when the layer's number of drawable descendants changes.
+  void AddDrawableDescendants(int num);
+
   void AddDependentNeedsPushProperties();
   void RemoveDependentNeedsPushProperties();
   bool parent_should_know_need_push_properties() const {
     return needs_push_properties() || descendant_needs_push_properties();
   }
 
   bool IsPropertyChangeAllowed() const;
 
   // If this layer has a scroll parent, it removes |this| from its list of
   // scroll children.
@@ skipping 73 matching lines @@
   scoped_refptr<LayerAnimationController> layer_animation_controller_;
 
   // Layer properties.
   gfx::Size bounds_;
 
   gfx::Vector2d scroll_offset_;
   // This variable indicates which ancestor layer (if any) whose size,
   // transformed relative to this layer, defines the maximum scroll offset for
   // this layer.
   int scroll_clip_layer_id_;
+  int num_descendants_that_draw_content_;
   bool should_scroll_on_main_thread_ : 1;
   bool have_wheel_event_handlers_ : 1;
   bool have_scroll_event_handlers_ : 1;
   bool user_scrollable_horizontal_ : 1;
   bool user_scrollable_vertical_ : 1;
   bool is_root_for_isolated_group_ : 1;
   bool is_container_for_fixed_position_layers_ : 1;
   bool is_drawable_ : 1;
+  bool draws_content_ : 1;
   bool hide_layer_and_subtree_ : 1;
   bool masks_to_bounds_ : 1;
   bool contents_opaque_ : 1;
   bool double_sided_ : 1;
   bool should_flatten_transform_ : 1;
   bool use_parent_backface_visibility_ : 1;
   bool draw_checkerboard_for_missing_tiles_ : 1;
   bool force_render_surface_ : 1;
   bool transform_is_invertible_ : 1;
   Region non_fast_scrollable_region_;
@@ skipping 29 matching lines @@
   DrawProperties<Layer> draw_properties_;
 
   PaintProperties paint_properties_;
 
   DISALLOW_COPY_AND_ASSIGN(Layer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_H_