Inform window manager about modal windows in mus+ash.

services/ui/ws/window_tree_client_unittest.cc

Index: services/ui/ws/window_tree_client_unittest.cc
diff --git a/services/ui/ws/window_tree_client_unittest.cc b/services/ui/ws/window_tree_client_unittest.cc
index edb216a1d20959de6ad5d7c522a7ca3134c5f490..ca7795348e3ed9c2e33a852b90a5b9a7ced39dcd 100644
--- a/services/ui/ws/window_tree_client_unittest.cc
+++ b/services/ui/ws/window_tree_client_unittest.cc
@@ -462,6 +462,11 @@ class TestWindowTreeClient : public mojom::WindowTreeClient,
       const base::Optional<std::vector<uint8_t>>& value) override {
     window_manager_client_->WmResponse(change_id, false);
   }
+  void WmSetModalType(uint32_t change_id,
+                      uint32_t window_id,
+                      ui::ModalType type) override {
+    window_manager_client_->WmResponse(change_id, false);
+  }
   void WmSetCanFocus(uint32_t window_id, bool can_focus) override {}
   void WmCreateTopLevelWindow(
       uint32_t change_id,