Makes windowserver not send messages during shutdown

services/ui/ws/window_server.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 "services/ui/ws/window_server.h"
 
 #include <set>
 #include <string>
 
 #include "base/logging.h"
@@ skipping 43 matching lines @@
       next_wm_change_id_(0),
       gpu_proxy_(new GpuServiceProxy(this)),
       window_manager_window_tree_factory_set_(this, &user_id_tracker_) {
   user_id_tracker_.AddObserver(this);
   OnUserIdAdded(user_id_tracker_.active_id());
 }
 
 WindowServer::~WindowServer() {
   in_destructor_ = true;
 
+  for (auto& pair : tree_map_)
+    pair.second->PrepareForWindowServerShutdown();
+
   // Destroys the window trees results in querying for the display. Tear down
   // the displays first so that the trees are notified of the display going
   // away while the display is still valid.
   display_manager_->DestroyAllDisplays();
 
   while (!tree_map_.empty())
     DestroyTree(tree_map_.begin()->second.get());
 
   display_manager_.reset();
 }
@@ skipping 756 matching lines @@
 void WindowServer::OnUserIdAdded(const UserId& id) {
   activity_monitor_map_[id] = base::MakeUnique<UserActivityMonitor>(nullptr);
 }
 
 void WindowServer::OnUserIdRemoved(const UserId& id) {
   activity_monitor_map_.erase(id);
 }
 
 }  // namespace ws
 }  // namespace ui