Add system modals to the proper container in mus+ash.

mash/simple_wm/simple_wm.cc

 // Copyright 2016 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 "mash/simple_wm/simple_wm.h"
 
 #include "base/observer_list.h"
 #include "base/strings/utf_string_conversions.h"
 #include "mash/simple_wm/move_event_handler.h"
 #include "ui/aura/client/aura_constants.h"
@@ skipping 406 matching lines @@
   return false;
 }
 
 bool SimpleWM::OnWmSetProperty(
     aura::Window* window,
     const std::string& name,
     std::unique_ptr<std::vector<uint8_t>>* new_data) {
   return true;
 }
 
+void SimpleWM::OnWmSetModalType(aura::Window* window, ui::ModalType type) {}
+
 void SimpleWM::OnWmSetCanFocus(aura::Window* window, bool can_focus) {}
 
 aura::Window* SimpleWM::OnWmCreateTopLevelWindow(
     ui::mojom::WindowType window_type,
     std::map<std::string, std::vector<uint8_t>>* properties) {
   aura::Window* client_window = new aura::Window(nullptr);
   SetWindowType(client_window, window_type);
   client_window->Init(ui::LAYER_NOT_DRAWN);
 
   views::Widget* frame_widget = new views::Widget;
@@ skipping 139 matching lines @@
 }
 
 void SimpleWM::OnWindowListViewItemActivated(aura::Window* window) {
   window->Show();
   aura::client::ActivationClient* activation_client =
       aura::client::GetActivationClient(window->GetRootWindow());
   activation_client->ActivateWindow(window);
 }
 
 }  // namespace simple_wm