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

components/mus/ws/window_tree_impl.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/ws/window_tree_impl.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 391 matching lines @@
   client_->OnWindowHierarchyChanged(
       MapWindowIdToClient(window), MapWindowIdToClient(new_parent_id),
       MapWindowIdToClient(old_parent_id), WindowsToWindowDatas(to_send));
   connection_manager_->OnConnectionMessagedClient(id_);
 }
 
 void WindowTreeImpl::ProcessWindowReorder(const ServerWindow* window,
                                           const ServerWindow* relative_window,
                                           mojom::OrderDirection direction,
                                           bool originated_change) {
+  DCHECK_EQ(window->parent(), relative_window->parent());
   if (originated_change || !IsWindowKnown(window) ||
       !IsWindowKnown(relative_window) ||
       connection_manager_->DidConnectionMessageClient(id_))
     return;
 
+  // Do not notify ordering changes of the root windows, since the client
+  // doesn't know about the ancestors of the roots, and so can't do anything
+  // about this ordering change of the root.
+  if (HasRoot(window) || HasRoot(relative_window))
+    return;
+
   client_->OnWindowReordered(MapWindowIdToClient(window),
                              MapWindowIdToClient(relative_window), direction);
   connection_manager_->OnConnectionMessagedClient(id_);
 }
 
 void WindowTreeImpl::ProcessWindowDeleted(const ServerWindow* window,
                                           bool originated_change) {
   if (window->id().connection_id == id_)
     window_map_.erase(window->id().window_id);
 
@@ skipping 724 matching lines @@
 
   for (const auto* root : roots_) {
     if (root->Contains(window))
       return true;
   }
   return false;
 }
 
 }  // namespace ws
 }  // namespace mus