Fix bug 1439650 - Track performance of all Ajax requests in Google An…

…alytics. (#878)

* Add start time to every ajax request.
* Send event to Google Analytics with the overall time of request and requested url.

.eslintrc.js

@@ -41,7 +41,8 @@ module.exports = {
         editor: false,
         DIFF_INSERT: false,
         DIFF_EQUAL: false,
-        DIFF_DELETE: false
+        DIFF_DELETE: false,
+        ga: false
     },
     plugins: [
         'react',

pontoon/base/static/js/main.js

@@ -621,6 +621,24 @@ var Pontoon = (function (my) {
 
 /* Main code */
 $(function() {
+  /*
+   * If Google Analytics is enabled, frontend will send additional about Ajax calls.
+   *
+   * To send an event to GA, We pass following informations:
+   * event category - hardcoded 'ajax' string.
+   * event action - hardcoded 'request' string.
+   * event label - contains url that was called by $.ajax() call.
+   *
+   * GA Analytics enriches every event with additional information like e.g. browser, resolution, country etc.
+   */
+  $(document).ajaxComplete(function(event, jqXHR, settings) {
+      if (typeof(ga) !== 'function') {
+        return;
+      }
+
+      ga('send', 'event', 'ajax', 'request', settings.url);
+  });
+
   Pontoon.NProgressBind();
 
   // Display any notifications