Inform window manager about modal windows 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 492bad06abb5038984d5eb5fcfc3c1c5a8e3ecba..79d1479466f26143d6ad9dc99172b6f1763c68d2 100644
--- a/services/ui/ws/window_server_test_base.cc
+++ b/services/ui/ws/window_server_test_base.cc
@@ -168,6 +168,13 @@ bool WindowServerTestBase::OnWmSetProperty(
              : true;
 }
 
+bool WindowServerTestBase::OnWmSetModalType(aura::Window* window,
+                                            ui::ModalType type) {
+  return window_manager_delegate_
+             ? window_manager_delegate_->OnWmSetModalType(window, type)
+             : true;
+}
+
 void WindowServerTestBase::OnWmSetCanFocus(aura::Window* window,
                                            bool can_focus) {
   if (window_manager_delegate_)