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

services/ui/ws/window_server_test_base.cc

Index: services/ui/ws/window_server_test_base.cc
diff --git a/services/ui/ws/window_server_test_base.cc b/services/ui/ws/window_server_test_base.cc
index 4cfacda169833b403a27987954366362f530abac..fa521b3f7096f83b58e47e9e2872997c975343ab 100644
--- a/services/ui/ws/window_server_test_base.cc
+++ b/services/ui/ws/window_server_test_base.cc
@@ -168,6 +168,12 @@ bool WindowServerTestBase::OnWmSetProperty(
              : true;
 }
 
+void WindowServerTestBase::OnWmSetModalType(aura::Window* window,
+                                            ui::ModalType type) {
+  if (window_manager_delegate_)
+    window_manager_delegate_->OnWmSetModalType(window, type);
+}
+
 void WindowServerTestBase::OnWmSetCanFocus(aura::Window* window,
                                            bool can_focus) {
   if (window_manager_delegate_)