cc: Clean up root_layer code in LTI

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 3485 matching lines @@
     // screen_space_transform_is_animating. So when we see a new animation get
     // activated, we need to update the draw properties on the active tree.
     active_tree()->set_needs_update_draw_properties();
     // Request another frame to run the next tick of the animation.
     SetNeedsOneBeginImplFrame();
   }
 }
 
 std::string LayerTreeHostImpl::LayerTreeAsJson() const {
   std::string str;
-  if (active_tree_->root_layer()) {
+  if (active_tree_->root_layer_for_testing()) {
     std::unique_ptr<base::Value> json(
-        active_tree_->root_layer()->LayerTreeAsJson());
+        active_tree_->root_layer_for_testing()->LayerTreeAsJson());
     base::JSONWriter::WriteWithOptions(
         *json, base::JSONWriter::OPTIONS_PRETTY_PRINT, &str);
   }
   return str;
 }
 
 void LayerTreeHostImpl::RegisterScrollbarAnimationController(
     int scroll_layer_id) {
   if (settings().scrollbar_animator == LayerTreeSettings::NO_ANIMATOR)
     return;
@@ skipping 491 matching lines @@
   return task_runner_provider_->HasImplThread();
 }
 
 bool LayerTreeHostImpl::CommitToActiveTree() const {
   // In single threaded mode we skip the pending tree and commit directly to the
   // active tree.
   return !task_runner_provider_->HasImplThread();
 }
 
 }  // namespace cc