restored GA to samples index (#1010)

web/samples_index/lib/src/templates.dart

@@ -39,6 +39,7 @@ String _indexHeader = '''
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <script src="packages/mdc_web/material-components-web.min.js"></script>
   <script defer src="main.dart.js"></script>
+  ${_googleAnalytics()}
 </head>
 ''';
 
@@ -53,6 +54,7 @@ String _descriptionHeader = '''
   <script src="packages/mdc_web/material-components-web.min.js"></script>
   <script src="https://kit.fontawesome.com/16cc04762e.js"></script>
   <script defer src="description.dart.js"></script>
+  ${_googleAnalytics()}
 </head>
 ''';
 
@@ -60,7 +62,7 @@ String _navbar = '''
 <div class="navbar">
   <a class="leading" href="./">
     <img src="images/logos/logo_lockup_flutter_horizontal_wht_96.png" />
-    <span class="title">Samples</span> 
+    <span class="title">Samples</span>
   </a>
   <div class="nav-items">
     <a href="https://flutter.dev/">Flutter Home</a>
@@ -71,7 +73,7 @@ String _navbar = '''
 
 String _footer = '''
 <div class="footer">
-  <span>© Flutter 2020</span>
+  <span>© Flutter ${DateTime.now().toUtc().year}</span>
 </div>
 ''';
 
@@ -230,3 +232,14 @@ String _descriptionScreenshots(Sample sample) {
 String _descriptionText(Sample sample) {
   return '<p>${sample.description}</p>';
 }
+
+String _googleAnalytics() {
+  return """
+<script async src="https://www.googletagmanager.com/gtag/js?id=UA-67589403-8"></script>
+  <script>
+    window.dataLayer = window.dataLayer || [];
+    function gtag(){dataLayer.push(arguments);}
+    gtag('js', new Date());
+    gtag('config', 'UA-67589403-8');
+  </script>""";
+}