cc: Clean up root_layer code in LTI

cc/test/fake_layer_tree_host_impl.cc

 // Copyright 2012 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/test/fake_layer_tree_host_impl.h"
 
 #include <stddef.h>
 
 #include "cc/animation/animation_host.h"
 #include "cc/test/begin_frame_args_test.h"
@@ skipping 86 matching lines @@
       num_children_that_draw_content;
   return num_children_that_draw_content + (layer->DrawsContent() ? 1 : 0);
 }
 
 void FakeLayerTreeHostImpl::UpdateNumChildrenAndDrawPropertiesForActiveTree() {
   UpdateNumChildrenAndDrawProperties(active_tree());
 }
 
 void FakeLayerTreeHostImpl::UpdateNumChildrenAndDrawProperties(
     LayerTreeImpl* layerTree) {
-  RecursiveUpdateNumChildren(layerTree->root_layer());
+  RecursiveUpdateNumChildren(layerTree->root_layer_for_testing());
   bool update_lcd_text = false;
   layerTree->BuildLayerListAndPropertyTreesForTesting();
   layerTree->UpdateDrawProperties(update_lcd_text);
 }
 
 }  // namespace cc