Fixing not working JS file from an extension tutorial

Change-Id: I6e279db73eefa378d00efc6ebbe6376374023fc2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2526400Reviewed-by: Kevin McNee <mcnee@chromium.org>
Reviewed-by: Paul Irish <paulirish@chromium.org>
Commit-Queue: Paul Irish <paulirish@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827212}

chrome/common/extensions/docs/examples/tutorials/get_started/options.js

@@ -4,8 +4,8 @@
 
 'use strict';
 
+let page = document.getElementById('buttonDiv');
 const kButtonColors = ['#3aa757', '#e8453c', '#f9bb2d', '#4688f1'];
-
 function constructOptions(kButtonColors) {
   for (let item of kButtonColors) {
     let button = document.createElement('button');