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.

[sky, 2016/01/12 22:36:08]

Document why. If window or relative_window is a root then the client can't see
above the window and so doesn't need to know about the change.

[sadrul, 2016/01/13 02:26:05]

Done.

+  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