Filter out webidl files based on special comments, and feature-gate webxr interfaces. (#34348)

* Filter out webidl files based on skip-if directives.

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

* script: Don't build XR functionality without webxr feature.

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

* Fix tidy.

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

* script: Adjust imports for file movement.

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

* Fix clippy.

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

* Formatting.

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

* Clean up webxr module import.

Co-authored-by: Samson <16504129+sagudev@users.noreply.github.com>
Signed-off-by: Josh Matthews <josh@joshmatthews.net>

---------

Signed-off-by: Josh Matthews <josh@joshmatthews.net>
Co-authored-by: Samson <16504129+sagudev@users.noreply.github.com>

components/script/dom/webxr/xrlayer.rs

@@ -0,0 +1,77 @@
+/* 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 canvas_traits::webgl::WebGLContextId;
+use dom_struct::dom_struct;
+use webxr_api::LayerId;
+
+use crate::dom::bindings::inheritance::Castable;
+use crate::dom::bindings::root::Dom;
+use crate::dom::eventtarget::EventTarget;
+use crate::dom::webglrenderingcontext::WebGLRenderingContext;
+use crate::dom::xrframe::XRFrame;
+use crate::dom::xrsession::XRSession;
+use crate::dom::xrwebgllayer::XRWebGLLayer;
+
+#[dom_struct]
+pub struct XRLayer {
+    event_target: EventTarget,
+    session: Dom<XRSession>,
+    context: Dom<WebGLRenderingContext>,
+    /// If none, the session is inline (the composition disabled flag is true)
+    /// and this is a XRWebGLLayer.
+    #[ignore_malloc_size_of = "Layer ids don't heap-allocate"]
+    #[no_trace]
+    layer_id: Option<LayerId>,
+}
+
+impl XRLayer {
+    #[allow(dead_code)]
+    pub fn new_inherited(
+        session: &XRSession,
+        context: &WebGLRenderingContext,
+        layer_id: Option<LayerId>,
+    ) -> XRLayer {
+        XRLayer {
+            event_target: EventTarget::new_inherited(),
+            session: Dom::from_ref(session),
+            context: Dom::from_ref(context),
+            layer_id,
+        }
+    }
+
+    pub(crate) fn layer_id(&self) -> Option<LayerId> {
+        self.layer_id
+    }
+
+    pub(crate) fn context_id(&self) -> WebGLContextId {
+        self.context.context_id()
+    }
+
+    pub(crate) fn context(&self) -> &WebGLRenderingContext {
+        &self.context
+    }
+
+    pub(crate) fn session(&self) -> &XRSession {
+        &self.session
+    }
+
+    pub fn begin_frame(&self, frame: &XRFrame) -> Option<()> {
+        // TODO: Implement this for other layer types
+        if let Some(this) = self.downcast::<XRWebGLLayer>() {
+            this.begin_frame(frame)
+        } else {
+            unimplemented!()
+        }
+    }
+
+    pub fn end_frame(&self, frame: &XRFrame) -> Option<()> {
+        // TODO: Implement this for other layer types
+        if let Some(this) = self.downcast::<XRWebGLLayer>() {
+            this.end_frame(frame)
+        } else {
+            unimplemented!()
+        }
+    }
+}