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

services/ui/ws/window_manager_client_unittest.cc

Index: services/ui/ws/window_manager_client_unittest.cc
diff --git a/services/ui/ws/window_manager_client_unittest.cc b/services/ui/ws/window_manager_client_unittest.cc
index 02a59a7096c0b0adeb056c7eb4e7079a2043c313..c23fbe4c3bbf2db8bdd1ec92fc9909ff07f2dacc 100644
--- a/services/ui/ws/window_manager_client_unittest.cc
+++ b/services/ui/ws/window_manager_client_unittest.cc
@@ -54,6 +54,7 @@ class TestWindowManagerDelegate : public aura::WindowManagerDelegate {
       std::unique_ptr<std::vector<uint8_t>>* new_data) override {
     return false;
   }
+  void OnWmSetModalType(aura::Window* window, ui::ModalType type) override {}
   void OnWmSetCanFocus(aura::Window* window, bool can_focus) override {}
   aura::Window* OnWmCreateTopLevelWindow(
       ui::mojom::WindowType window_type,