hello_base_view.txt

main
    scenic::CreateScenicSessionPtrAndListenerRequest(scenic.get()),
        scenic->CreateSession(session.NewRequest(), listener_handle.Bind());
            In scenic process:
            CreateSessionImmediately(std::move(session_request), std::move(listener));

    ShadertoyEmbedderView::ShadertoyEmbedderView
        BaseView::BaseView(
            View::View
                session->Enqueue(NewCreateViewCmd(id(), std::move(token), debug_name));
                    SystemTypeForCmd(cmd);
                    SessionHandler::DispatchCommand
                        buffered_commands_.emplace_back(std::move(command.gfx()));
                            把createview cmd放入buffer

    root_presenter->PresentView(std::move(view_holder_token), nullptr);
        ===>
        转入root presenter进程, see root_presenter.txt

    view->LaunchShadertoyClient();
        LaunchAppAndCreateView("shadertoy_client");
            zx::eventpair::create(0u, &view_holder_token, &view_token);
                view event pair用于连接在不同进程中的2个view, 把child view放到viewholder里
                viewholder要后创建，创建时会去找child view


            info.view_provider->CreateView(std::move(view_token),
                                 info.services_from_child_view.NewRequest(),
                                 std::move(services_to_child_view));
                rpc调用shadertoy里的CreateView
这里也没有进入present循环