Add an unobtrusive log when server disconnects

packages/react-dev-utils/webpackHotDevClient.js

@@ -130,9 +130,15 @@ var connection = new SockJS(url.format({
   // Hardcoded in WebpackDevServer
   pathname: '/sockjs-node'
 }));
-// Note: unlike WebpackDevServer's built-in client,
-// we don't handle disconnect. If connection fails,
-// just leave it instead of spamming the console.
+
+// Unlike WebpackDevServer client, we won't try to reconnect
+// to avoid spamming the console. Disconnect usually happens
+// when developer stops the server.
+connection.onclose = function() {
+  console.info(
+    'The development server has disconnected.\nRefresh the page if necessary.'
+  );
+};
 
 // Remember some state related to hot module replacement.
 var isFirstCompilation = true;