cc: Make occlusion a draw property.

cc/trees/layer_tree_impl.h

 // Copyright 2012 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_TREES_LAYER_TREE_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 202 matching lines @@
   void ForceRedrawNextActivation() { next_activation_forces_redraw_ = true; }
 
   void set_has_ever_been_drawn(bool has_drawn) {
     has_ever_been_drawn_ = has_drawn;
   }
   bool has_ever_been_drawn() const { return has_ever_been_drawn_; }
 
   void set_ui_resource_request_queue(const UIResourceRequestQueue& queue);
 
   const LayerImplList& RenderSurfaceLayerList() const;
+  const Region& UnoccludedScreenSpaceRegion() const;
 
   // These return the size of the root scrollable area and the size of
   // the user-visible scrolling viewport, in CSS layout coordinates.
   gfx::Size ScrollableSize() const;
   gfx::SizeF ScrollableViewportSize() const;
 
   gfx::Rect RootScrollLayerDeviceViewportBounds() const;
 
   LayerImpl* LayerById(int id);
 
@@ skipping 141 matching lines @@
   LayerIdMap layer_id_map_;
 
   std::vector<PictureLayerImpl*> picture_layers_;
   std::vector<LayerImpl*> layers_with_copy_output_request_;
 
   // Persisted state for non-impl-side-painting.
   int scrolling_layer_id_from_previous_tree_;
 
   // List of visible layers for the most recently prepared frame.
   LayerImplList render_surface_layer_list_;
+  // After drawing the |render_surface_layer_list_| the areas in this region
+  // would not be fully covered by opaque content.
+  Region unoccluded_screen_space_region_;
 
   bool contents_textures_purged_;
   bool viewport_size_invalid_;
   bool needs_update_draw_properties_;
 
   // In impl-side painting mode, this is true when the tree may contain
   // structural differences relative to the active tree.
   bool needs_full_tree_sync_;
 
   bool next_activation_forces_redraw_;
@@ skipping 18 matching lines @@
 
   scoped_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_