Function find_main_render_widget 

unsafe fn find_main_render_widget(
    root: *mut c_void,
    pane_outer_hwnds: &[*mut c_void],
) -> Option<*mut c_void>

Walk descendants of root and return the first Chrome_RenderWidgetHostHWND whose ancestor chain does NOT pass through any of pane_outer_hwnds. Panes are siblings of main under the Views top-level, so without this filter the walk would happily pick a pane’s render widget.