libservo: Expose a ServoBuilder (#36549)

Expose a `ServoBuilder` for easily creating Servo instances using
default values. This change enables removing `EmbedderTraits`.

Testing: This is covered by `Servo` unit tests.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

ports/servoshell/desktop/webxr.rs

@@ -0,0 +1,78 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use std::cell::RefCell;
+use std::rc::Rc;
+
+use servo::config::pref;
+use servo::config::prefs::Preferences;
+use servo::webxr::WebXrRegistry;
+use servo::webxr::glwindow::GlWindowDiscovery;
+#[cfg(target_os = "windows")]
+use servo::webxr::openxr::{AppInfo, OpenXrDiscovery};
+use winit::event_loop::ActiveEventLoop;
+
+use super::window_trait::WindowPortsMethods;
+
+#[cfg(feature = "webxr")]
+enum XrDiscovery {
+    GlWindow(GlWindowDiscovery),
+    #[cfg(target_os = "windows")]
+    OpenXr(OpenXrDiscovery),
+}
+
+#[cfg(feature = "webxr")]
+pub(crate) struct XrDiscoveryWebXrRegistry {
+    xr_discovery: RefCell<Option<XrDiscovery>>,
+}
+
+impl XrDiscoveryWebXrRegistry {
+    pub(crate) fn new_boxed(
+        window: Rc<dyn WindowPortsMethods>,
+        event_loop: Option<&ActiveEventLoop>,
+        preferences: &Preferences,
+    ) -> Box<Self> {
+        let Some(event_loop) = event_loop else {
+            return Box::new(Self {
+                xr_discovery: RefCell::new(None),
+            });
+        };
+
+        let xr_discovery = if preferences.dom_webxr_openxr_enabled {
+            #[cfg(target_os = "windows")]
+            {
+                let app_info = AppInfo::new("Servoshell", 0, "Servo", 0);
+                Some(XrDiscovery::OpenXr(OpenXrDiscovery::new(None, app_info)))
+            }
+            #[cfg(not(target_os = "windows"))]
+            None
+        } else if preferences.dom_webxr_glwindow_enabled {
+            let window = window.new_glwindow(event_loop);
+            Some(XrDiscovery::GlWindow(GlWindowDiscovery::new(window)))
+        } else {
+            None
+        };
+
+        Box::new(Self {
+            xr_discovery: RefCell::new(xr_discovery),
+        })
+    }
+}
+
+#[cfg(feature = "webxr")]
+impl WebXrRegistry for XrDiscoveryWebXrRegistry {
+    fn register(&self, xr: &mut servo::webxr::MainThreadRegistry) {
+        use servo::webxr::headless::HeadlessMockDiscovery;
+
+        if pref!(dom_webxr_test) {
+            xr.register_mock(HeadlessMockDiscovery::default());
+        } else if let Some(xr_discovery) = self.xr_discovery.take() {
+            match xr_discovery {
+                XrDiscovery::GlWindow(discovery) => xr.register(discovery),
+                #[cfg(target_os = "windows")]
+                XrDiscovery::OpenXr(discovery) => xr.register(discovery),
+            }
+        }
+    }
+}