device_runner.txt

启动的是userpicker_device_shell.
ermine_user_shell会生成device_shell_config.json，
userpicker_device_shell会读这个文件，启动ermine_user_shell


modular::DeviceRunnerApp app(settings, context, [&loop, &cobalt_cleanup] {
    cobalt_cleanup.call();
    loop.Quit();
});
  Start()
    std::make_unique<AppClient<fuchsia::modular::Lifecycle>>(context_->launcher().get(), CloneStruct(settings_.device_shell));
      device_shell是"userpicker_device_shell"
      appclient会通过service_连接device shell服务。

      launch_info.directory_request = services_.NewRequest();
      launcher->CreateComponent(std::move(launch_info), app_.NewRequest());
        把userpicker_device_shell启动起来
      services().ConnectToService(service_.NewRequest());
        连接device shell里的LifeCycle服务

    device_shell_app_->services().ConnectToService(device_shell_.NewRequest());
      device_shell_通向device shell里的device shell服务了

    device_shell_app_->services().ConnectToService(device_shell_view_provider.NewRequest());
      向device shell服务要device shell view服务。