add toggle decorations action

winit/src/application.rs

@@ -660,6 +660,9 @@ pub fn run_command<A, E>(
                 window::Action::ToggleMaximize => {
                     window.set_maximized(!window.is_maximized())
                 }
+                window::Action::ToggleDecorations => {
+                    window.set_decorations(!window.is_decorated())
+                }
                 window::Action::FetchMode(tag) => {
                     let mode = if window.is_visible().unwrap_or(true) {
                         conversion::mode(window.fullscreen())