Some code review changes.

src/lib/utils.js

@@ -2,6 +2,8 @@
 
 import { Tinode } from 'tinode-sdk';
 
+import { CALL_MESSAGE_MIME_TYPE } from '../constants.js'
+
 // Make shortcut icon appear with a green dot + show unread count in title.
 export function updateFavicon(count) {
   const oldIcon = document.getElementById('shortcut-icon');
@@ -208,7 +210,7 @@ export function cancelablePromise(promise) {
 
 // Returns true if specified mime type represents a Tinode video call.
 export function isVideoCall(mime) {
-  return mime == 'application/tinode-video-call';
+  return mime == CALL_MESSAGE_MIME_TYPE;
 }
 
 // Clips string to the specified length.