Add stubs for session start/end

components/script/dom/webidls/XRSession.webidl

@@ -33,7 +33,7 @@ interface XRSession : EventTarget {
   long requestAnimationFrame(XRFrameRequestCallback callback);
   void cancelAnimationFrame(long handle);
 
-  // Promise<void> end();
+  Promise<void> end();
 
   // // Events
   // attribute EventHandler onblur;

components/script/dom/webidls/XRTest.webidl

@@ -16,7 +16,7 @@ interface XRTest {
   void simulateUserActivation(Function f);
 
   // // Disconnect all fake devices
-  // Promise<void> disconnectAllDevices();
+  Promise<void> disconnectAllDevices();
 };
 
 dictionary FakeXRDeviceInit {

components/script/dom/xrsession.rs

@@ -288,6 +288,14 @@ impl XRSessionMethods for XRSession {
             .map(|x| DomRoot::from_ref(&**x))
             .collect()
     }
+
+    /// https://immersive-web.github.io/webxr/#dom-xrsession-end
+    fn End(&self) -> Rc<Promise> {
+        // XXXManishearth implement device disconnection and session ending
+        let p = Promise::new(&self.global());
+        p.resolve_native(&());
+        p
+    }
 }
 
 #[derive(Clone, Copy, Debug)]

components/script/dom/xrtest.rs

@@ -170,4 +170,12 @@ impl XRTestMethods for XRTest {
         // XXXManishearth actually check for activation in XRSession
         let _ = f.Call__(vec![], ExceptionHandling::Rethrow);
     }
+
+    /// https://github.com/immersive-web/webxr-test-api/blob/master/explainer.md
+    fn DisconnectAllDevices(&self) -> Rc<Promise> {
+        // XXXManishearth implement device disconnection and session ending
+        let p = Promise::new(&self.global());
+        p.resolve_native(&());
+        p
+    }
 }