Remove usage of private method 'div' in automerger

Google-Bug-Id: b/199777213
Change-Id: Icbe2f6b51625fe707c9c8054359ffcd026e4dca3

src/main/resources/static/automerger.js

diff --git a/src/main/resources/static/automerger.js b/src/main/resources/static/automerger.js
index d1df593..67ec7b8 100644
--- a/src/main/resources/static/automerger.js
+++ b/src/main/resources/static/automerger.js
@@ -42,7 +42,11 @@
         // Create actual merge button
         var b = createMergeButton(c, branchToCheckbox);
         var popupElements = checkboxes.concat(b);
-        c.popup(c.div.apply(this, popupElements));
+        const div = document.createElement('div');
+        for (const el of popupElements) {
+          div.appendChild(el);
+        }
+        c.popup(div);
         return branchToCheckbox;
     }