UMA metric for LayerUpdateTimes

cc/trees/layer_tree.h

 // Copyright 2016 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.
 
 #ifndef CC_TREES_LAYER_TREE_H_
 #define CC_TREES_LAYER_TREE_H_
 
 #include <memory>
 #include <unordered_map>
 #include <unordered_set>
@@ skipping 123 matching lines @@
 
   void SetNeedsCommit();
 
   const LayerTreeSettings& GetSettings() const;
 
   // Methods which should only be used internally in cc ------------------
   void RegisterLayer(Layer* layer);
   void UnregisterLayer(Layer* layer);
   Layer* LayerById(int id) const;
 
+  size_t NumLayers() const;
+
   bool UpdateLayers(const LayerList& update_layer_list,
                     bool* content_is_suitable_for_gpu);
   bool in_paint_layer_contents() const { return in_paint_layer_contents_; }
 
   void AddLayerShouldPushProperties(Layer* layer);
   void RemoveLayerShouldPushProperties(Layer* layer);
   std::unordered_set<Layer*>& LayersThatShouldPushProperties();
   bool LayerNeedsPushPropertiesForTesting(Layer* layer) const;
 
   virtual void SetNeedsMetaInfoRecomputation(
@@ skipping 151 matching lines @@
   // external embedder.
   EnginePictureCache* engine_picture_cache_;
   ClientPictureCache* client_picture_cache_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTree);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_H_