test(aio): cleaner approach to reliable Google Analytics e2e tests (#20661)

PR Close #20661

aio/e2e/app.e2e-spec.ts

@@ -80,8 +80,6 @@ describe('site App', function() {
     });
   });
 
-  // TODO(https://github.com/angular/angular/issues/19785): Activate this again
-  // once it is no more flaky.
   describe('google analytics', () => {
 
     it('should call ga with initial URL', done => {

aio/e2e/app.po.ts

@@ -29,10 +29,7 @@ export class SitePage {
   locationPath() { return browser.executeScript('return document.location.pathname') as promise.Promise<string>; }
 
   navigateTo(pageUrl = '') {
-    return browser.get('/' + pageUrl)
-      // We need to tell the index.html not to load the real analytics library
-      // See the GA snippet in index.html
-      .then(() => browser.executeScript('sessionStorage.setItem("__e2e__", true);'));
+    return browser.get('/' + pageUrl);
   }
 
   getDocViewerText() {

aio/src/index.html

@@ -34,11 +34,13 @@
 
   <!-- Google Analytics -->
   <script>
-  // Note this is a customised version of the GA tracking snippet to aid e2e testing
-  // See the bit between /**/.../**/
+  // Note this is a customised version of the GA tracking snippet
+  // See the comments below for more info
   (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;/**/i.sessionStorage.__e2e__||/**/m.parentNode.insertBefore(a,m)
+  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;
+  ~i.name.indexOf('NG_DEFER_BOOTSTRAP')|| // only load library if not running e2e tests
+  m.parentNode.insertBefore(a,m)
   })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
   </script>
   <!-- End Google Analytics -->