cc: Add initial GPU-to-GPU copy rasterizer implementation.

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index a1f4fae0a4f3901f0890c361f74a0c67b8dc62a0..71b7989abb23c98b7d5c4bcd00b0829e7bb254be 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -470,6 +470,7 @@ class CC_EXPORT LayerTreeHostImpl
   void CreateAndSetTileManager(ResourceProvider* resource_provider,
                                ContextProvider* context_provider,
                                bool using_map_image,
+                               bool use_staging_pool,
                                bool allow_rasterize_on_demand);
   void ReleaseTreeResources();
   void EnforceZeroBudget(bool zero_budget);
@@ -544,6 +545,7 @@ class CC_EXPORT LayerTreeHostImpl
   scoped_ptr<RasterWorkerPool> raster_worker_pool_;
   scoped_ptr<RasterWorkerPool> direct_raster_worker_pool_;
   scoped_ptr<ResourcePool> resource_pool_;
+  scoped_ptr<ResourcePool> staging_resource_pool_;
   scoped_ptr<Renderer> renderer_;
 
   GlobalStateThatImpactsTilePriority global_tile_state_;