Google analytics tracking

Summary:
Adds tracking for:
- short URL created
- value in interactive documentation changed

Reviewed By: priteshrnandgaonkar

Differential Revision: D7123493

fbshipit-source-id: 2fc19fa6c9b5614043af508a82e898b3ccefcbaa

website/src/components/DocsSidebar.js

@@ -50,7 +50,17 @@ export default class DocsSidebar extends Component<Props> {
           <EditValue
             property={prop}
             value={props.layout[prop]}
-            onChange={props.onChange}
+            onChange={(property, value) => {
+              if (window.ga) {
+                window.ga('send', {
+                  hitType: 'event',
+                  eventCategory: 'DocsSidebar',
+                  eventAction: 'valueChanged',
+                  eventLabel: prop,
+                });
+              }
+              props.onChange(property, value);
+            }}
           />,
           element,
         );

website/src/components/Playground/URLShortener.js

@@ -45,6 +45,14 @@ export default class URLShortener extends Component<{}, State> {
         loading: true,
       },
       () => {
+        if (window.ga) {
+          window.ga('send', {
+            hitType: 'event',
+            eventCategory: 'URLShortener',
+            eventAction: 'created'
+          });
+        }
+
         fetch(`https://www.googleapis.com/urlshortener/v1/url?key=${API_KEY}`, {
           method: 'POST',
           headers: {