cc : Move LayerImpl::children to test properties

cc/test/fake_layer_tree_host_impl.cc

Index: cc/test/fake_layer_tree_host_impl.cc
diff --git a/cc/test/fake_layer_tree_host_impl.cc b/cc/test/fake_layer_tree_host_impl.cc
index 81f816c192c9fa3d62e6b2dbbbd39fe3cb2817f7..a0b9f48647e9f531105a5e362565c9c91a06beeb 100644
--- a/cc/test/fake_layer_tree_host_impl.cc
+++ b/cc/test/fake_layer_tree_host_impl.cc
@@ -89,9 +89,9 @@ void FakeLayerTreeHostImpl::AdvanceToNextFrame(base::TimeDelta advance_by) {
 
 int FakeLayerTreeHostImpl::RecursiveUpdateNumChildren(LayerImpl* layer) {
   int num_children_that_draw_content = 0;
-  for (size_t i = 0; i < layer->children().size(); ++i) {
+  for (size_t i = 0; i < layer->test_properties()->children.size(); ++i) {
     num_children_that_draw_content +=
-        RecursiveUpdateNumChildren(layer->children()[i]);
+        RecursiveUpdateNumChildren(layer->test_properties()->children[i]);
   }
   layer->test_properties()->num_descendants_that_draw_content =
       num_children_that_draw_content;