Hook up prefetcher settings

Summary: This makes use of the previously set up new settings. The logic is a tiny bit difficult to follow so I wanted to make sure it's not lost in the noise of the previous diff.

Reviewed By: jknoxville

Differential Revision: D18036538

fbshipit-source-id: db3bbce4361862cee479aed70578a4bcbde2c46d

src/fb-stubs/Prefetcher.tsx

@@ -7,5 +7,7 @@
  * @format
  */
 
-export default async function setupPrefetcher() {}
+import {Settings} from '../reducers/settings';
+
+export default async function setupPrefetcher(_settings: Settings) {}
 export const shouldInstallPrefetcher = () => false;