chromeos: Makes AshTestBase/Helper target mash when appropriate

ash/mus/window_manager.cc

Index: ash/mus/window_manager.cc
diff --git a/ash/mus/window_manager.cc b/ash/mus/window_manager.cc
index 27315befbecd62722af5b14f070d44d9a441b508..26879415f2f793a6fcd7aa06b6c8d56fddd16721 100644
--- a/ash/mus/window_manager.cc
+++ b/ash/mus/window_manager.cc
@@ -195,7 +195,8 @@ void WindowManager::CreateShell(
       WmWindow::Get(window_tree_host->window()),
       shell_delegate_for_test_ ? std::move(shell_delegate_for_test_)
                                : base::MakeUnique<ShellDelegateMus>(connector_),
-      this, pointer_watcher_event_router_.get());
+      this, pointer_watcher_event_router_.get(),
+      create_session_state_delegate_stub_for_test_);
   init_params.primary_window_tree_host = window_tree_host.release();
   init_params.wm_shell = wm_shell;
   init_params.blocking_pool = blocking_pool_.get();