Require IssuableDiscussions component and implement loading template.

src/webview/src/App.vue

 <script>
 import IssuableDetails from './components/IssuableDetails';
+import IssuableDiscussions from './components/IssuableDiscussions';
 
 export default {
   name: 'app',
   data() {
     return {
-      issuable: {
-        title: 'Loading...',
-      },
+      isLoading: false,
+      issuable: {},
       discussions: [],
     };
   },
   components: {
     IssuableDetails,
+    IssuableDiscussions,
   },
   created() {
+    this.isLoading = true;
+
     window.addEventListener('message', event => {
       this.issuable = event.data.issuable;
+      this.isLoading = false;
     });
   },
 }
@@ -24,8 +28,11 @@ export default {
 
 <template>
   <div id="app">
-    <issuable-details :issuable="issuable" />
-    <issuable-discussions :discussions="discussions" />
+    <h2 v-if="isLoading">Loading...</h2>
+    <template v-else>
+      <issuable-details :issuable="issuable" />
+      <issuable-discussions :discussions="discussions" />
+    </template>
   </div>
 </template>