cc: Make sure we don't insert or remove layers during painting

cc/trees/layer_tree_host.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.h"
 
 #include <algorithm>
 #include <stack>
 #include <string>
 
@@ skipping 1078 matching lines @@
                                    main_frame_events.Pass());
 }
 
 Layer* LayerTreeHost::LayerById(int id) const {
   LayerIdMap::const_iterator iter = layer_id_map_.find(id);
   return iter != layer_id_map_.end() ? iter->second : NULL;
 }
 
 void LayerTreeHost::RegisterLayer(Layer* layer) {
   DCHECK(!LayerById(layer->id()));
+  DCHECK(!in_paint_layer_contents_);
   layer_id_map_[layer->id()] = layer;
   if (animation_host_)
     animation_host_->RegisterLayer(layer->id(), LayerTreeType::ACTIVE);
 }
 
 void LayerTreeHost::UnregisterLayer(Layer* layer) {
   DCHECK(LayerById(layer->id()));
+  DCHECK(!in_paint_layer_contents_);
   if (animation_host_)
     animation_host_->UnregisterLayer(layer->id(), LayerTreeType::ACTIVE);
   layer_id_map_.erase(layer->id());
 }
 
 bool LayerTreeHost::IsLayerInTree(int layer_id, LayerTreeType tree_type) const {
   return tree_type == LayerTreeType::ACTIVE;
 }
 
 void LayerTreeHost::SetMutatorsNeedCommit() {
@@ skipping 91 matching lines @@
   return animation_host_ ? animation_host_->HasAnyAnimation(layer->id())
                          : false;
 }
 
 bool LayerTreeHost::HasActiveAnimation(const Layer* layer) const {
   return animation_host_ ? animation_host_->HasActiveAnimation(layer->id())
                          : false;
 }
 
 }  // namespace cc