Keeping track of descendants that draw content instead of recalcualting

cc/layers/layer.h

Index: cc/layers/layer.h
diff --git a/cc/layers/layer.h b/cc/layers/layer.h
index ab897a8ac9914ab08085ab45aa8b1ea8fa4ababf..2b6de6514aba996af23d16f1dd9d5987cbc0238c 100644
--- a/cc/layers/layer.h
+++ b/cc/layers/layer.h
@@ -352,6 +352,7 @@ class CC_EXPORT Layer : public base::RefCounted<Layer>,
 
   // These methods typically need to be overwritten by derived classes.
   virtual bool DrawsContent() const;
+  virtual int NumDescendantsThatDrawContent() const;
   virtual void SavePaintProperties();
   // Returns true iff any resources were updated that need to be committed.
   virtual bool Update(ResourceUpdateQueue* queue,
@@ -460,6 +461,12 @@ class CC_EXPORT Layer : public base::RefCounted<Layer>,
   void Set3dSortingContextId(int id);
   int sorting_context_id() const { return sorting_context_id_; }
 
+  // Called when our number of Drawable Descendants changes

[danakj, 2014/07/14 15:49:23]

nit: s/D/d/g and add a .

[awoloszyn, 2014/07/14 19:38:33]

Done.

+  void AddDrawableDescendants(int num);

[danakj, 2014/07/14 15:49:23]

Can these all be protected?

[awoloszyn, 2014/07/14 19:38:33]

Done.

+  void RemoveDrawableDescendants(int num);
+
+  void SetDrawsContent(bool draws_content);
+
  protected:
   friend class LayerImpl;
   friend class TreeSynchronizer;
@@ -486,6 +493,9 @@ class CC_EXPORT Layer : public base::RefCounted<Layer>,
   // unused resources on the impl thread are returned before commit completes.
   void SetNextCommitWaitsForActivation();
 
+  // Will relcalculate whether or not we draw content and set draws_content_
+  // appropriately.
+  virtual void UpdateDrawsContent(bool draws_content);
   void AddDependentNeedsPushProperties();
   void RemoveDependentNeedsPushProperties();
   bool parent_should_know_need_push_properties() const {
@@ -579,6 +589,7 @@ class CC_EXPORT Layer : public base::RefCounted<Layer>,
   // 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;
@@ -587,6 +598,7 @@ class CC_EXPORT Layer : public base::RefCounted<Layer>,
   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;