Add more out of line copy ctors for complex classes.

cc/layers/layer_list_iterator.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/layers/layer_list_iterator.h"
 
 #include "cc/layers/layer_impl.h"
 
 namespace cc {
 
 LayerListIterator::LayerListIterator(LayerImpl* root_layer)
     : current_layer_(root_layer) {
   DCHECK(!root_layer || !root_layer->parent());
   list_indices_.push_back(0);
 }
 
+LayerListIterator::LayerListIterator(const LayerListIterator& other) = default;
+
 LayerListIterator::~LayerListIterator() {}
 
 LayerListIterator& LayerListIterator::operator++() {
   // case 0: done
   if (!current_layer_)
     return *this;
 
   // case 1: descend.
   const LayerImplList& current_list = current_layer_->children();
   if (!current_list.empty()) {
@@ skipping 60 matching lines @@
   if (current_list.empty())
     return;
 
   size_t last_index = current_list.size() - 1;
   current_layer_ = current_list[last_index];
   list_indices_.push_back(last_index);
   DescendToRightmostInSubtree();
 }
 
 }  // namespace cc