UMA metric for LayerUpdateTimes

cc/trees/layer_tree.cc

 // 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.
 
 #include "cc/trees/layer_tree.h"
 
 #include "base/auto_reset.h"
 #include "base/time/time.h"
 #include "cc/input/page_scale_animation.h"
 #include "cc/layers/heads_up_display_layer.h"
@@ skipping 223 matching lines @@
   }
   RemoveLayerShouldPushProperties(layer);
   layer_id_map_.erase(layer->id());
 }
 
 Layer* LayerTree::LayerById(int id) const {
   LayerIdMap::const_iterator iter = layer_id_map_.find(id);
   return iter != layer_id_map_.end() ? iter->second : nullptr;
 }
 
+size_t LayerTree::NumLayers() const {
+  return layer_id_map_.size();
+}
+
 bool LayerTree::UpdateLayers(const LayerList& update_layer_list,
                              bool* content_is_suitable_for_gpu) {
   base::AutoReset<bool> painting(&in_paint_layer_contents_, true);
   bool did_paint_content = false;
   for (const auto& layer : update_layer_list) {
     did_paint_content |= layer->Update();
     *content_is_suitable_for_gpu &= layer->IsSuitableForGpuRasterization();
   }
   return did_paint_content;
 }
@@ skipping 325 matching lines @@
 LayerListReverseIterator<Layer> LayerTree::rend() {
   return LayerListReverseIterator<Layer>(nullptr);
 }
 
 void LayerTree::SetNeedsDisplayOnAllLayers() {
   for (auto* layer : *this)
     layer->SetNeedsDisplay();
 }
 
 }  // namespace cc