mus: Do not notify clients when the roots are reordered.

components/mus/public/cpp/lib/window.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 "components/mus/public/cpp/window.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <set>
@@ skipping 760 matching lines @@
 
 // static
 // Returns true if the order actually changed.
 bool Window::ReorderImpl(Window* window,
                          Window* relative,
                          mojom::OrderDirection direction,
                          OrderChangedNotifier* notifier) {
   DCHECK(relative);
   DCHECK_NE(window, relative);
   DCHECK_EQ(window->parent(), relative->parent());
+  DCHECK(window->parent());
 
   if (!AdjustStackingForTransientWindows(&window, &relative, &direction,
                                          window->stacking_target_))
     return false;
 
   const size_t child_i = std::find(window->parent_->children_.begin(),
                                    window->parent_->children_.end(), window) -
                          window->parent_->children_.begin();
   const size_t target_i =
       std::find(window->parent_->children_.begin(),
@@ skipping 21 matching lines @@
     notifier->NotifyWindowReordered();
 
   return true;
 }
 
 // static
 Window** Window::GetStackingTarget(Window* window) {
   return &window->stacking_target_;
 }
 }  // namespace mus