Trigger Node destruction notifications from Node's dtor

mojo/services/view_manager/node_delegate.h

 // 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.
 
 #ifndef MOJO_SERVICES_VIEW_MANAGER_NODE_DELEGATE_H_
 #define MOJO_SERVICES_VIEW_MANAGER_NODE_DELEGATE_H_
 
 #include "mojo/services/view_manager/view_manager_export.h"
 
 namespace ui {
 class Event;
 }
 
 namespace gfx {
 class Rect;
 }
 
 namespace mojo {
 namespace view_manager {
 namespace service {
 
 class Node;
 class View;
 
 class MOJO_VIEW_MANAGER_EXPORT NodeDelegate {
  public:
+  // Invoked at the end of the Node's destructor (after it has been removed from
+  // the hierarchy and its active view has been reset).
+  virtual void OnNodeDestroyed(const Node* node) = 0;
+
   // Invoked when the hierarchy has changed.
   virtual void OnNodeHierarchyChanged(const Node* node,
                                       const Node* new_parent,
                                       const Node* old_parent) = 0;
 
   virtual void OnNodeBoundsChanged(const Node* node,
                                    const gfx::Rect& old_bounds,
                                    const gfx::Rect& new_bounds) = 0;
 
   // Invoked when the View associated with a node changes.
   virtual void OnNodeViewReplaced(const Node* node,
                                   const View* new_view,
                                   const View* old_view) = 0;
 
   // Invoked when an input event is received by the View at this node.
   virtual void OnViewInputEvent(const View* view,
                                 const ui::Event* event) = 0;
 
  protected:
   virtual ~NodeDelegate() {}
 };
 
 }  // namespace service
 }  // namespace view_manager
 }  // namespace mojo
 
 #endif  // MOJO_SERVICES_VIEW_MANAGER_NODE_DELEGATE_H_