Add google analytics. (#5438)

docs/_layouts/user-guide.html

@@ -7,6 +7,13 @@
   <meta http-equiv="X-UA-Compatible" content="IE=edge">
   <link rel="stylesheet" href="{{ '/assets/css/style.css?v=' | append: site.github.build_revision | relative_url }}">
   <link rel="stylesheet" type="text/css" href="{{ '/assets/css/print.css' | relative_url }}" media="print">
+  <script async src="https://www.googletagmanager.com/gtag/js?id=G-TMTZVLLMBP"></script>
+  <script>
+    window.dataLayer = window.dataLayer || [];
+    function gtag(){dataLayer.push(arguments);}
+    gtag('js', new Date());
+    gtag('config', 'G-TMTZVLLMBP');
+  </script>
   <!--[if lt IE 9]>
     <script src="//html5shiv.googlecode.com/svn/trunk/html5.js"></script>
     <![endif]-->
@@ -407,19 +414,6 @@
     });
   </script>
   <script id="MathJax-script" async src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script>
-
-  {% if site.google_analytics %}
-  <script>
-    (function (i, s, o, g, r, a, m) {
-      i['GoogleAnalyticsObject'] = r; i[r] = i[r] || function () {
-        (i[r].q = i[r].q || []).push(arguments)
-      }, i[r].l = 1 * new Date(); a = s.createElement(o),
-        m = s.getElementsByTagName(o)[0]; a.async = 1; a.src = g; m.parentNode.insertBefore(a, m)
-    })(window, document, 'script', '//www.google-analytics.com/analytics.js', 'ga');
-    ga('create', '{{ site.google_analytics }}', 'auto');
-    ga('send', 'pageview');
-  </script>
-  {% endif %}
 </body>
 
 </html>