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

cc/trees/layer_tree_host_common_perftest.cc

Index: cc/trees/layer_tree_host_common_perftest.cc
diff --git a/cc/trees/layer_tree_host_common_perftest.cc b/cc/trees/layer_tree_host_common_perftest.cc
index 1ec729269b2bcff198e26da8a0202607821e2c47..260e574381db9a60e89c6a1a6ff6f049683b2835 100644
--- a/cc/trees/layer_tree_host_common_perftest.cc
+++ b/cc/trees/layer_tree_host_common_perftest.cc
@@ -178,12 +178,10 @@ class BspTreePerfTest : public CalcDrawPropsTest {
   }
 
   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);
+      }
     }
   }