cc : Determine if a layer is root by using the value in LayerTreeImpl

cc/trees/layer_tree_host_impl.cc

 // 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.
 
 #include "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 791 matching lines @@
   // Create the render passes in dependency order.
   size_t render_surface_layer_list_size =
       frame->render_surface_layer_list->size();
   for (size_t i = 0; i < render_surface_layer_list_size; ++i) {
     size_t surface_index = render_surface_layer_list_size - 1 - i;
     LayerImpl* render_surface_layer =
         (*frame->render_surface_layer_list)[surface_index];
     RenderSurfaceImpl* render_surface = render_surface_layer->render_surface();
 
     bool should_draw_into_render_pass =
-        render_surface_layer->parent() == NULL ||
+        active_tree_->IsRootLayer(render_surface_layer) ||
         render_surface->contributes_to_drawn_surface() ||
         render_surface_layer->HasCopyRequest();
     if (should_draw_into_render_pass)
       render_surface->AppendRenderPasses(frame);
   }
 
   // When we are displaying the HUD, change the root damage rect to cover the
   // entire root surface. This will disable partial-swap/scissor optimizations
   // that would prevent the HUD from updating, since the HUD does not cause
   // damage itself, to prevent it from messing with damage visualizations. Since
@@ skipping 3099 matching lines @@
   return task_runner_provider_->HasImplThread();
 }
 
 bool LayerTreeHostImpl::CommitToActiveTree() const {
   // In single threaded mode we skip the pending tree and commit directly to the
   // active tree.
   return !task_runner_provider_->HasImplThread();
 }
 
 }  // namespace cc