is_foreground_window stubs for other backends

druid-shell/src/backend/gtk/window.rs

@@ -1056,6 +1056,10 @@ impl WindowHandle {
         }
     }
 
+    pub fn is_foreground_window(&self) -> bool {
+        true
+    }
+
     pub fn set_window_state(&mut self, size_state: window::WindowState) {
         use window::WindowState::{Maximized, Minimized, Restored};
         let cur_size_state = self.get_window_state();

druid-shell/src/backend/mac/window.rs

@@ -1362,6 +1362,10 @@ impl WindowHandle {
         }
     }
 
+    pub fn is_foreground_window(&self) -> bool {
+        true
+    }
+
     pub fn get_window_state(&self) -> WindowState {
         unsafe {
             let window: id = msg_send![*self.nsview.load(), window];

druid-shell/src/backend/wayland/window.rs

@@ -134,6 +134,10 @@ impl WindowHandle {
         self.inner.surface.get_size()
     }
 
+    pub fn is_foreground_window(&self) -> bool {
+        true
+    }
+
     pub fn set_window_state(&mut self, _current_state: window::WindowState) {
         tracing::warn!("set_window_state is unimplemented on wayland");
     }

druid-shell/src/backend/web/window.rs

@@ -528,6 +528,10 @@ impl WindowHandle {
         Size::new(0.0, 0.0)
     }
 
+    pub fn is_foreground_window(&self) -> bool {
+        true
+    }
+
     pub fn content_insets(&self) -> Insets {
         warn!("WindowHandle::content_insets unimplemented for web.");
         Insets::ZERO

druid-shell/src/backend/x11/window.rs

@@ -1718,6 +1718,10 @@ impl WindowHandle {
         }
     }
 
+    pub fn is_foreground_window(&self) -> bool {
+        true
+    }
+
     pub fn set_window_state(&self, _state: window::WindowState) {
         warn!("WindowHandle::set_window_state is currently unimplemented for X11 backend.");
     }