aura-mus: Implement Deactivate().

services/ui/public/cpp/tests/test_window_tree.h

Index: services/ui/public/cpp/tests/test_window_tree.h
diff --git a/services/ui/public/cpp/tests/test_window_tree.h b/services/ui/public/cpp/tests/test_window_tree.h
index 81b5bfcb703c341eff0e661d1948f1e7eb5f6d44..594dbd22add6a89c61c63f917eaf580dbd6ec221 100644
--- a/services/ui/public/cpp/tests/test_window_tree.h
+++ b/services/ui/public/cpp/tests/test_window_tree.h
@@ -102,6 +102,7 @@ class TestWindowTree : public mojom::WindowTree {
                         mojo::TextInputStatePtr state) override;
   void OnWindowInputEventAck(uint32_t event_id,
                              ui::mojom::EventResult result) override;
+  void DeactivateWindow(uint32_t window_id) override;
   void GetWindowManagerClient(
       mojo::AssociatedInterfaceRequest<mojom::WindowManagerClient> internal)
       override;