cc: Clean up root_layer code in LTI

cc/layers/heads_up_display_layer_impl_unittest.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 <stddef.h>
 
 #include "cc/layers/append_quads_data.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
 #include "cc/test/fake_impl_task_runner_provider.h"
 #include "cc/test/fake_layer_tree_host_impl.h"
@@ skipping 31 matching lines @@
                                   &task_graph_runner);
   host_impl.CreatePendingTree();
   host_impl.SetVisible(true);
   host_impl.InitializeRenderer(output_surface.get());
   std::unique_ptr<HeadsUpDisplayLayerImpl> layer_ptr =
       HeadsUpDisplayLayerImpl::Create(host_impl.pending_tree(), 1);
   layer_ptr->SetBounds(gfx::Size(100, 100));
 
   HeadsUpDisplayLayerImpl* layer = layer_ptr.get();
 
-  host_impl.pending_tree()->SetRootLayer(std::move(layer_ptr));
+  host_impl.pending_tree()->SetRootLayerForTesting(std::move(layer_ptr));
   host_impl.pending_tree()->BuildLayerListAndPropertyTreesForTesting();
 
   // Check regular hardware draw is ok.
   CheckDrawLayer(layer, host_impl.resource_provider(), DRAW_MODE_HARDWARE);
 
   // Simulate a resource loss on transitioning to resourceless software mode.
   layer->ReleaseResources();
 
   // Should skip resourceless software draw and not crash in UpdateHudTexture.
   CheckDrawLayer(layer, host_impl.resource_provider(),
                  DRAW_MODE_RESOURCELESS_SOFTWARE);
 }
 
 }  // namespace
 }  // namespace cc