webdriver: Implement support for simple dialogs (#37913)

Implement webdriver user prompt: accept alert, dismiss alert, get alert
text.

Tests:
https://github.com/longvatrong111/servo/actions/runs/16175408035
https://github.com/longvatrong111/servo/actions/runs/16175409545

Signed-off-by: batu_hoang <longvatrong111@gmail.com>

ports/servoshell/desktop/app.rs

@@ -27,7 +27,8 @@ use servo::webrender_api::ScrollLocation;
 use servo::webrender_api::units::DeviceIntSize;
 use servo::{
     EventLoopWaker, InputEvent, KeyboardEvent, MouseButtonEvent, MouseMoveEvent,
-    WebDriverCommandMsg, WebDriverScriptCommand, WheelDelta, WheelEvent, WheelMode,
+    WebDriverCommandMsg, WebDriverScriptCommand, WebDriverUserPromptAction, WheelDelta, WheelEvent,
+    WheelMode,
 };
 use url::Url;
 use winit::application::ApplicationHandler;
@@ -552,6 +553,35 @@ impl App {
                         webdriver_script_command,
                     ));
                 },
+                WebDriverCommandMsg::HandleUserPrompt(webview_id, action, response_sender) => {
+                    let response = if running_state.webview_has_active_dialog(webview_id) {
+                        match action {
+                            WebDriverUserPromptAction::Accept => {
+                                running_state.accept_active_dialogs(webview_id)
+                            },
+                            WebDriverUserPromptAction::Dismiss => {
+                                running_state.dismiss_active_dialogs(webview_id)
+                            },
+                        };
+                        Ok(())
+                    } else {
+                        Err(())
+                    };
+
+                    if let Err(error) = response_sender.send(response) {
+                        warn!("Failed to send response of HandleUserPrompt: {error}");
+                    };
+                },
+                WebDriverCommandMsg::GetAlertText(webview_id, response_sender) => {
+                    let response = match running_state.alert_text_of_newest_dialog(webview_id) {
+                        Some(text) => Ok(text),
+                        None => Err(()),
+                    };
+
+                    if let Err(error) = response_sender.send(response) {
+                        warn!("Failed to send response of GetAlertText: {error}");
+                    };
+                },
                 WebDriverCommandMsg::TakeScreenshot(..) => {
                     warn!(
                         "WebDriverCommand {:?} is still not moved from constellation to embedder",

ports/servoshell/desktop/app_state.rs

@@ -337,6 +337,38 @@ impl RunningAppState {
             .is_some_and(|dialogs| !dialogs.is_empty())
     }
 
+    pub(crate) fn webview_has_active_dialog(&self, webview_id: WebViewId) -> bool {
+        let inner = self.inner();
+        inner
+            .dialogs
+            .get(&webview_id)
+            .is_some_and(|dialogs| !dialogs.is_empty())
+    }
+
+    pub(crate) fn accept_active_dialogs(&self, webview_id: WebViewId) {
+        if let Some(dialogs) = self.inner_mut().dialogs.get_mut(&webview_id) {
+            dialogs.drain(..).for_each(|dialog| {
+                dialog.accept();
+            });
+        }
+    }
+
+    pub(crate) fn dismiss_active_dialogs(&self, webview_id: WebViewId) {
+        if let Some(dialogs) = self.inner_mut().dialogs.get_mut(&webview_id) {
+            dialogs.drain(..).for_each(|dialog| {
+                dialog.dismiss();
+            });
+        }
+    }
+
+    pub(crate) fn alert_text_of_newest_dialog(&self, webview_id: WebViewId) -> Option<String> {
+        self.inner()
+            .dialogs
+            .get(&webview_id)
+            .and_then(|dialogs| dialogs.last())
+            .and_then(|dialog| dialog.message())
+    }
+
     pub(crate) fn get_focused_webview_index(&self) -> Option<usize> {
         let focused_id = self.inner().focused_webview_id?;
         self.webviews()
@@ -486,6 +518,17 @@ impl WebViewDelegate for RunningAppState {
     fn show_simple_dialog(&self, webview: servo::WebView, dialog: SimpleDialog) {
         self.interrupt_webdriver_script_evaluation();
 
+        // Dialogs block the page load, so need need to notify WebDriver
+        let webview_id = webview.id();
+        if let Some(sender) = self
+            .webdriver_senders
+            .borrow_mut()
+            .load_status_senders
+            .get(&webview_id)
+        {
+            let _ = sender.send(WebDriverLoadStatus::Blocked);
+        };
+
         if self.servoshell_preferences.headless &&
             self.servoshell_preferences.webdriver_port.is_none()
         {

ports/servoshell/desktop/dialog.rs

@@ -140,6 +140,34 @@ impl Dialog {
         }
     }
 
+    pub fn accept(&self) {
+        #[allow(clippy::single_match)]
+        match self {
+            Dialog::SimpleDialog(dialog) => {
+                dialog.accept();
+            },
+            _ => {},
+        }
+    }
+
+    pub fn dismiss(&self) {
+        #[allow(clippy::single_match)]
+        match self {
+            Dialog::SimpleDialog(dialog) => {
+                dialog.dismiss();
+            },
+            _ => {},
+        }
+    }
+
+    pub fn message(&self) -> Option<String> {
+        #[allow(clippy::single_match)]
+        match self {
+            Dialog::SimpleDialog(dialog) => Some(dialog.message().to_string()),
+            _ => None,
+        }
+    }
+
     pub fn update(&mut self, ctx: &egui::Context) -> bool {
         match self {
             Dialog::File {