Remove OnRootRemoved from ViewManagerDelegate

mojo/services/public/cpp/view_manager/view_manager_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_PUBLIC_CPP_VIEW_MANAGER_VIEW_MANAGER_DELEGATE_H_
 #define MOJO_SERVICES_PUBLIC_CPP_VIEW_MANAGER_VIEW_MANAGER_DELEGATE_H_
 
 namespace mojo {
 namespace view_manager {
 
 class Node;
 class ViewManager;
 
 class ViewManagerDelegate {
  public:
   virtual void OnRootAdded(ViewManager* view_manager, Node* root) {}
-  virtual void OnRootRemoved(ViewManager* view_manager, Node* root) {}
 
  protected:
   virtual ~ViewManagerDelegate() {}
 };
 
 }  // namespace view_manager
 }  // namespace mojo
 
 #endif  // MOJO_SERVICES_PUBLIC_CPP_VIEW_MANAGER_VIEW_MANAGER_DELEGATE_H_