Provide a no-op SW that will be served by the dev environment. (facebook#2276)

* Provide a no-op SW that will be served by the dev environment.

* Hide no-op service worker from user

Author: jeffposnick

config/webpackDevServer.config.js

@@ -11,6 +11,7 @@
 'use strict';
 
 const errorOverlayMiddleware = require('react-error-overlay/middleware');
+const noopServiceWorkerMiddleware = require('react-dev-utils/noopServiceWorkerMiddleware');
 const config = require('./webpack.config.dev');
 const paths = require('./paths');
 
@@ -90,6 +91,12 @@ module.exports = function(proxy, allowedHost) {
     setup(app) {
       // This lets us open files from the runtime error overlay.
       app.use(errorOverlayMiddleware());
+      // This service worker file is effectively a 'no-op' that will reset any
+      // previous service worker registered for the same host:port combination.
+      // We do this in development to avoid hitting the production cache if
+      // it used the same host and port.
+      // https://github.com/facebookincubator/create-react-app/issues/2272#issuecomment-302832432
+      app.use(noopServiceWorkerMiddleware());
     },
   };
 };