Initial attempt at counting layers in the compositor thread.

cc/trees/layer_tree_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_impl.h"
 
 #include <limits>
 #include <set>
 
 #include "base/debug/trace_event.h"
@@ skipping 543 matching lines @@
 void LayerTreeImpl::RegisterLayer(LayerImpl* layer) {
   DCHECK(!LayerById(layer->id()));
   layer_id_map_[layer->id()] = layer;
 }
 
 void LayerTreeImpl::UnregisterLayer(LayerImpl* layer) {
   DCHECK(LayerById(layer->id()));
   layer_id_map_.erase(layer->id());
 }
 
+size_t LayerTreeImpl::NumLayers() {
+  return layer_id_map_.size();
+}
+
 void LayerTreeImpl::PushPersistedState(LayerTreeImpl* pending_tree) {
   pending_tree->SetCurrentlyScrollingLayer(
       LayerTreeHostCommon::FindLayerInSubtree(pending_tree->root_layer(),
           currently_scrolling_layer_ ? currently_scrolling_layer_->id() : 0));
 }
 
 static void DidBecomeActiveRecursive(LayerImpl* layer) {
   layer->DidBecomeActive();
   for (size_t i = 0; i < layer->children().size(); ++i)
     DidBecomeActiveRecursive(layer->children()[i]);
@@ skipping 797 matching lines @@
 
 void LayerTreeImpl::UnregisterPictureLayerImpl(PictureLayerImpl* layer) {
   layer_tree_host_impl_->UnregisterPictureLayerImpl(layer);
 }
 
 void LayerTreeImpl::InputScrollAnimationFinished() {
   layer_tree_host_impl_->ScrollEnd();
 }
 
 }  // namespace cc