Provide an API to the example window manager app that supports closing a window.

mojo/services/public/cpp/view_manager/lib/view_manager_private.cc

 // Copyright 2014 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 "mojo/services/public/cpp/view_manager/lib/view_manager_private.h"
 
 #include "mojo/services/public/cpp/view_manager/lib/view_tree_node_private.h"
 #include "mojo/services/public/cpp/view_manager/view_tree_node_observer.h"
 
 namespace mojo {
@@ skipping 32 matching lines @@
 void ViewManagerPrivate::AddRoot(ViewTreeNode* root) {
   // A new root must not already exist as a root or be contained by an existing
   // hierarchy visible to this view manager.
   std::vector<ViewTreeNode*>::const_iterator it = manager_->roots().begin();
   for (; it != manager_->roots().end(); ++it) {
     if (*it == root || (*it)->Contains(root))
       return;
   }
   manager_->roots_.push_back(root);
   root->AddObserver(new RootObserver(root));
-  manager_->root_added_callback_.Run(manager_);
+  if (!manager_->root_added_callback_.is_null())
+    manager_->root_added_callback_.Run(manager_, root);
 }
 
 void ViewManagerPrivate::RemoveRoot(ViewTreeNode* root) {
   std::vector<ViewTreeNode*>::iterator it =
       std::find(manager_->roots_.begin(), manager_->roots_.end(), root);
-  if (it != manager_->roots_.end())
+  if (it != manager_->roots_.end()) {
     manager_->roots_.erase(it);
+    if (!manager_->root_removed_callback_.is_null())
+      manager_->root_removed_callback_.Run(manager_, root);
+  }
 }
 
 void ViewManagerPrivate::AddNode(TransportNodeId node_id, ViewTreeNode* node) {
   DCHECK(!manager_->nodes_[node_id]);
   manager_->nodes_[node_id] = node;
 }
 
 void ViewManagerPrivate::RemoveNode(TransportNodeId node_id) {
   ViewManager::IdToNodeMap::iterator it = manager_->nodes_.find(node_id);
   if (it != manager_->nodes_.end())
     manager_->nodes_.erase(it);
 }
 
 void ViewManagerPrivate::AddView(TransportViewId view_id, View* view) {
   DCHECK(!manager_->views_[view_id]);
   manager_->views_[view_id] = view;
 }
 
 void ViewManagerPrivate::RemoveView(TransportViewId view_id) {
   ViewManager::IdToViewMap::iterator it = manager_->views_.find(view_id);
   if (it != manager_->views_.end())
     manager_->views_.erase(it);
 }
 
 }  // namespace view_manager
 }  // namespace mojo