cc: Remove LayerImpl::children() calls from descendants of LayerTreeTest

cc/trees/layer_tree_host_common_perftest.cc

 // Copyright 2013 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 <stddef.h>
 
 #include <deque>
 #include <memory>
 #include <sstream>
 
@@ skipping 160 matching lines @@
         }
       }
       BspTree bsp_tree(&test_list);
       timer_.NextLap();
     } while (!timer_.HasTimeLimitExpired());
 
     EndTest();
   }
 
   void BuildLayerImplList(LayerImpl* layer, LayerImplList* list) {
-    if (layer->Is3dSorted() && !layer->bounds().IsEmpty()) {
-      list->push_back(layer);
-    }
-
-    for (size_t i = 0; i < layer->children().size(); i++) {
-      BuildLayerImplList(layer->children()[i], list);
+    for (auto* layer_impl : *layer->layer_tree_impl()) {
+      if (layer_impl->Is3dSorted() && !layer_impl->bounds().IsEmpty()) {
+        list->push_back(layer_impl);
+      }
     }
   }
 
  private:
   LayerImplList base_list_;
   int num_duplicates_;
 };
 
 TEST_F(CalcDrawPropsTest, TenTen) {
   SetTestName("10_10");
@@ skipping 54 matching lines @@
 
 TEST_F(BspTreePerfTest, BspTreeCubes_4) {
   SetTestName("bsp_tree_cubes_4");
   SetNumberOfDuplicates(4);
   ReadTestFile("layer_sort_cubes");
   RunSortLayers();
 }
 
 }  // namespace
 }  // namespace cc