services/session: Extract windowEventWatcherTask

This just calls `waitForEvent()` for now, same as before.

Author: Turbo87

app/services/session.js

@@ -72,7 +72,7 @@ export default class SessionService extends Service {
     let { url } = await ajax(`/api/private/session/begin`);
     win.location = url;
 
-    let event = await race([waitForEvent(window, 'message'), this.windowCloseWatcherTask.perform(win)]);
+    let event = await race([this.windowEventWatcherTask.perform(), this.windowCloseWatcherTask.perform(win)]);
     if (event.closed) {
       this.notifications.warning('Login was canceled because the popup window was closed.');
       return;
@@ -111,6 +111,10 @@ export default class SessionService extends Service {
     }
   });
 
+  windowEventWatcherTask = task(async () => {
+    return await waitForEvent(window, 'message');
+  });
+
   windowCloseWatcherTask = task(async window => {
     // eslint-disable-next-line no-constant-condition
     while (true) {