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

ui/aura/test/aura_test_base.cc

 // Copyright (c) 2012 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 "ui/aura/test/aura_test_base.h"
 
 #include "ui/aura/client/window_parenting_client.h"
 #include "ui/aura/mus/property_utils.h"
 #include "ui/aura/mus/window_tree_client.h"
 #include "ui/aura/mus/window_tree_host_mus.h"
@@ skipping 151 matching lines @@
   return true;
 }
 
 bool AuraTestBase::OnWmSetProperty(
     Window* window,
     const std::string& name,
     std::unique_ptr<std::vector<uint8_t>>* new_data) {
   return true;
 }
 
+void AuraTestBase::OnWmSetModalType(Window* window, ui::ModalType type) {}
+
 void AuraTestBase::OnWmSetCanFocus(Window* window, bool can_focus) {}
 
 Window* AuraTestBase::OnWmCreateTopLevelWindow(
     ui::mojom::WindowType window_type,
     std::map<std::string, std::vector<uint8_t>>* properties) {
   Window* window = new Window(nullptr);
   SetWindowType(window, window_type);
   window->Init(ui::LAYER_NOT_DRAWN);
   return window;
 }
@@ skipping 67 matching lines @@
 
 AuraTestBaseMus::~AuraTestBaseMus() {}
 
 void AuraTestBaseMus::SetUp() {
   ConfigureBackend(test::BackendType::MUS);
   AuraTestBase::SetUp();
 }
 
 }  // namespace test
 }  // namespace aura