views/mus: Recreate WindowManagerConnection for each test.

ui/views/mus/window_manager_connection.cc

Index: ui/views/mus/window_manager_connection.cc
diff --git a/ui/views/mus/window_manager_connection.cc b/ui/views/mus/window_manager_connection.cc
index 9954f9ea3dd890a9473fbfd70bf91b1945157539..d9a32889c151d013bede8ddf4da5068a93cc45fd 100644
--- a/ui/views/mus/window_manager_connection.cc
+++ b/ui/views/mus/window_manager_connection.cc
@@ -129,6 +129,11 @@ WindowManagerConnection::~WindowManagerConnection() {
   client_.reset();
   if (created_device_data_manager_)
     ui::DeviceDataManager::DeleteInstance();
+
+  if (ViewsDelegate::GetInstance()) {
+    ViewsDelegate::GetInstance()->set_native_widget_factory(
+        ViewsDelegate::NativeWidgetFactory());
+  }
 }
 
 bool WindowManagerConnection::HasPointerWatcher() {