Change clientApiDelegate from a class to a object.

This is because the media app attempts to use the spread operator on the
class which, due to the typescript compilation step which targets ES5,
doesn't handle the class instance correctly.

Bug: 996088
Change-Id: Idfb4e00aa29c40864fecf7d5ee777d470f40566d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2098192Reviewed-by: Trent Apted <tapted@chromium.org>
Commit-Queue: Zain Afzal <zafzal@google.com>
Cr-Commit-Position: refs/heads/master@{#749558}

chromeos/components/media_app_ui/resources/js/receiver.js

@@ -69,13 +69,13 @@ parentMessagePipe.registerHandler(Message.LOAD_FILE, (message) => {
 /**
  * A delegate which exposes privileged WebUI functionality to the media
  * app.
- * @implements mediaApp.ClientApiDelegate
+ * @type {!mediaApp.ClientApiDelegate}
  */
-class Delegate {
+const DELEGATE = {
   /** @override */
   async openFeedbackDialog() {
-    const response = await parentMessagePipe.sendMessage(
-      Message.OPEN_FEEDBACK_DIALOG);
+    const response =
+        await parentMessagePipe.sendMessage(Message.OPEN_FEEDBACK_DIALOG);
     return /** @type {?string} */ (response['errorMessage']);
   }
 };
@@ -113,7 +113,7 @@ async function loadFile(token, file) {
  * @param {!mediaApp.ClientApi} app
  */
 function initializeApp(app) {
-  app.setDelegate(new Delegate());
+  app.setDelegate(DELEGATE);
 }
 
 /**