cc: Clean up root_layer code in LTI

cc/test/fake_layer_tree_host.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 "cc/test/fake_layer_tree_host.h"
 
 #include "base/memory/ptr_util.h"
 #include "cc/animation/animation_host.h"
 #include "cc/layers/layer.h"
 #include "cc/test/fake_image_serialization_processor.h"
@@ skipping 85 matching lines @@
   if (page_scale_layer() && inner_viewport_scroll_layer()) {
     active_tree()->SetViewportLayersFromIds(
         overscroll_elasticity_layer() ? overscroll_elasticity_layer()->id()
                                       : Layer::INVALID_ID,
         page_scale_layer()->id(), inner_viewport_scroll_layer()->id(),
         outer_viewport_scroll_layer() ? outer_viewport_scroll_layer()->id()
                                       : Layer::INVALID_ID);
   }
 
   active_tree()->UpdatePropertyTreesForBoundsDelta();
-  return active_tree()->root_layer();
+  return active_tree()->root_layer_for_testing();
 }
 
 LayerImpl* FakeLayerTreeHost::CommitAndCreatePendingTree() {
   TreeSynchronizer::SynchronizeTrees(root_layer(), pending_tree());
   pending_tree()->SetPropertyTrees(property_trees());
   TreeSynchronizer::PushLayerProperties(root_layer()->layer_tree_host(),
                                         pending_tree());
   animation_host()->PushPropertiesTo(host_impl_.animation_host());
 
   pending_tree()->UpdatePropertyTreeScrollOffset(property_trees());
-  return pending_tree()->root_layer();
+  return pending_tree()->root_layer_for_testing();
 }
 
 }  // namespace cc