Add GA event to State selection (Fixes #782) (#808)

* Switch back to CDN.

* Add GA event to State selection.

* Add explanatory comment to state selector.

* Improve event action text for state selection.

frontend/src/components/Selectors/StateSelector.tsx

@@ -1,6 +1,7 @@
 import { DropDownMenu } from 'material-ui/DropDownMenu'
 import MenuItem from 'material-ui/MenuItem'
 import * as React from 'react'
+import * as ReactGA from 'react-ga'
 import { State, STATES } from '../../constants/states'
 import { Store } from '../../services/store'
 
@@ -10,6 +11,10 @@ type StateSelectorProps = {
   store: Store
 }
 
+/**
+ * This State Selector is used to select a state to view for US-wide datasets. These datasets
+ * include points for the entire US and allow the user to select which states to view.
+ */
 export let StateSelector: React.StatelessComponent<StateSelectorProps> = ({ className, store, value }) =>
   <DropDownMenu
     className={className ? className : undefined}
@@ -21,7 +26,15 @@ export let StateSelector: React.StatelessComponent<StateSelectorProps> = ({ clas
     )}
   </DropDownMenu >
 
+/**
+ * As part of State selection, send an event to GA.
+ */
 function onStateChange(value: State, store: Store) {
+  ReactGA.event({
+    category: 'Filter',
+    action: 'Selected a state in a US-wide dataset',
+    label: value.toString()
+  })
   store.set('selectedState')(value)
   store.set('useCustomCountyUpload')(false)
   store.set('selectedCounties')(null)