pub(crate) fn create_constellation(
    user_agent: Cow<'static, str>,
    config_dir: Option<PathBuf>,
    embedder_proxy: EmbedderProxy,
    compositor_proxy: CompositorProxy,
    time_profiler_chan: ProfilerChan,
    mem_profiler_chan: ProfilerChan,
    devtools_sender: Option<Sender<DevtoolsControlMsg>>,
    webrender_document: DocumentId,
    webrender_api_sender: RenderApiSender,
    webxr_registry: Registry,
    player_context: WindowGLContext,
    webgl_threads: Option<WebGLThreads>,
    glplayer_threads: Option<GLPlayerThreads>,
    initial_window_size: WindowSizeData,
    external_images: Arc<Mutex<WebrenderExternalImageRegistry>>,
    wgpu_image_map: Arc<Mutex<HashMap<u64, PresentationData>>>
) -> Sender<ConstellationMsg>