Function layout_document 

pub fn layout_document<T: ParsedFontTrait + Sync + 'static>(
    cache: &mut LayoutCache,
    text_cache: &mut TextLayoutCache,
    new_dom: &StyledDom,
    viewport: LogicalRect,
    font_manager: &FontManager<T>,
    scroll_offsets: &BTreeMap<NodeId, ScrollPosition>,
    text_selections: &BTreeMap<DomId, TextSelection>,
    debug_messages: &mut Option<Vec<LayoutDebugMessage>>,
    gpu_value_cache: Option<&GpuValueCache>,
    renderer_resources: &RendererResources,
    id_namespace: IdNamespace,
    dom_id: DomId,
    cursor_is_visible: bool,
    cursor_locations: Vec<(DomId, NodeId, TextCursor)>,
    preedit_text: Option<String>,
    image_cache: &ImageCache,
    system_style: Option<Arc<SystemStyle>>,
    get_system_time_fn: GetSystemTimeCallback,
) -> Result<DisplayList>