Revert of cc : Make LayerImpl destruction independent of tree hierarchy

cc/trees/damage_tracker_unittest.cc

Index: cc/trees/damage_tracker_unittest.cc
diff --git a/cc/trees/damage_tracker_unittest.cc b/cc/trees/damage_tracker_unittest.cc
index 687951794fab25964b62474a87af6379bdf3bedd..0101d0b8af325db3d3792925626d5b4121d333ab 100644
--- a/cc/trees/damage_tracker_unittest.cc
+++ b/cc/trees/damage_tracker_unittest.cc
@@ -83,7 +83,7 @@
                    &task_graph_runner_) {}
 
   LayerImpl* CreateTestTreeWithOneSurface() {
-    host_impl_.active_tree()->DetachLayers();
+    host_impl_.active_tree()->ClearLayers();
     std::unique_ptr<LayerImpl> root =
         LayerImpl::Create(host_impl_.active_tree(), 1);
     std::unique_ptr<LayerImpl> child =
@@ -108,7 +108,7 @@
     // child1. Additionally, the root has a second child layer, and child1 has
     // two children of its own.
 
-    host_impl_.active_tree()->DetachLayers();
+    host_impl_.active_tree()->ClearLayers();
     std::unique_ptr<LayerImpl> root =
         LayerImpl::Create(host_impl_.active_tree(), 1);
     std::unique_ptr<LayerImpl> child1 =