cc: Clean up root_layer code in LTI

cc/input/scrollbar_animation_controller_linear_fade_unittest.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/input/scrollbar_animation_controller_linear_fade.h"
 
 #include "cc/layers/solid_color_scrollbar_layer_impl.h"
 #include "cc/test/fake_impl_task_runner_provider.h"
 #include "cc/test/fake_layer_tree_host_impl.h"
 #include "cc/test/geometry_test_utils.h"
@@ skipping 46 matching lines @@
             kTrackStart, kIsLeftSideVerticalScrollbar, kIsOverlayScrollbar);
     scrollbar_layer_ = scrollbar.get();
     scrollbar_layer_->test_properties()->opacity_can_animate = true;
     std::unique_ptr<LayerImpl> clip =
         LayerImpl::Create(host_impl_.active_tree(), 3);
     clip_layer_ = clip.get();
     scroll_layer->SetScrollClipLayer(clip_layer_->id());
     LayerImpl* scroll_layer_ptr = scroll_layer.get();
     scroll_layer->test_properties()->AddChild(std::move(scrollbar));
     clip->test_properties()->AddChild(std::move(scroll_layer));
-    host_impl_.active_tree()->SetRootLayer(std::move(clip));
+    host_impl_.active_tree()->SetRootLayerForTesting(std::move(clip));
 
     scrollbar_layer_->SetScrollLayerId(scroll_layer_ptr->id());
     clip_layer_->SetBounds(gfx::Size(100, 100));
     scroll_layer_ptr->SetBounds(gfx::Size(200, 200));
     host_impl_.active_tree()->BuildLayerListAndPropertyTreesForTesting();
 
     scrollbar_controller_ = ScrollbarAnimationControllerLinearFade::Create(
         scroll_layer_ptr->id(), this, base::TimeDelta::FromSeconds(2),
         base::TimeDelta::FromSeconds(5), base::TimeDelta::FromSeconds(3));
   }
@@ skipping 404 matching lines @@
   EXPECT_FLOAT_EQ(1, scrollbar_layer_->Opacity());
 
   time += base::TimeDelta::FromSeconds(1);
   scrollbar_controller_->DidScrollEnd();
   EXPECT_FALSE(did_request_animate_);
   EXPECT_FLOAT_EQ(1, scrollbar_layer_->Opacity());
 }
 
 }  // namespace
 }  // namespace cc