cc: Address comments for https://codereview.chromium.org/1287043002/

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 <algorithm>
 #include <limits>
 #include <map>
 #include <set>
@@ skipping 2132 matching lines @@
 }
 
 void LayerTreeHostImpl::CleanUpTileManager() {
   tile_manager_->FinishTasksAndCleanUp();
   resource_pool_ = nullptr;
   tile_task_worker_pool_ = nullptr;
   single_thread_synchronous_task_graph_runner_ = nullptr;
 }
 
 scoped_ptr<OutputSurface> LayerTreeHostImpl::ReleaseOutputSurface() {
+  TRACE_EVENT0("cc", "LayerTreeHostImpl::ReleaseOutputSurface");
+
   // Since we will create a new resource provider, we cannot continue to use
   // the old resources (i.e. render_surfaces and texture IDs). Clear them
   // before we destroy the old resource provider.
   ReleaseTreeResources();
 
   // Note: order is important here.
   renderer_ = nullptr;
   CleanUpTileManager();
   resource_provider_ = nullptr;
 
@@ skipping 1435 matching lines @@
   if (active_tree()) {
     LayerAnimationValueProvider* layer = active_tree()->LayerById(layer_id);
     if (layer)
       return layer->ScrollOffsetForAnimation();
   }
 
   return gfx::ScrollOffset();
 }
 
 }  // namespace cc