Remove the default HMR error overlay (#4020)

This is supplied by webpack-hot-middleware.
I also added a test case to prevent this from popping up again.

client/webpack-hot-middleware-client.js

@@ -1,5 +1,5 @@
 import 'event-source-polyfill'
-import webpackHotMiddlewareClient from 'webpack-hot-middleware/client?autoConnect=false'
+import webpackHotMiddlewareClient from 'webpack-hot-middleware/client?autoConnect=false&overlay=false&reload=true'
 import Router from '../lib/router'
 
 const {
@@ -10,8 +10,6 @@ const {
 
 export default () => {
   webpackHotMiddlewareClient.setOptionsAndConnect({
-    overlay: 'false',
-    reload: 'true',
     path: `${assetPrefix}/_next/webpack-hmr`
   })
 

test/integration/basic/test/error-recovery.js

@@ -1,7 +1,7 @@
 /* global describe, it, expect */
 import webdriver from 'next-webdriver'
 import { join } from 'path'
-import { check, File } from 'next-test-utils'
+import { check, File, waitFor } from 'next-test-utils'
 
 export default (context, render) => {
   describe('Error Recovery', () => {
@@ -29,6 +29,30 @@ export default (context, render) => {
       browser.close()
     })
 
+    it('should not show the default HMR error overlay', async() => {
+      const browser = await webdriver(context.appPort, '/hmr/about')
+      const text = await browser
+        .elementByCss('p').text()
+      expect(text).toBe('This is the about page.')
+
+      const aboutPage = new File(join(__dirname, '../', 'pages', 'hmr', 'about.js'))
+      aboutPage.replace('</div>', 'div')
+
+      await check(
+        () => browser.elementByCss('body').text(),
+        /Unterminated JSX contents/
+      )
+
+      await waitFor(2000)
+
+      // Check for the error overlay
+      const bodyHtml = await browser.elementByCss('body').getAttribute('innerHTML')
+      expect(bodyHtml.includes('webpack-hot-middleware-clientOverlay')).toBeFalsy()
+
+      aboutPage.restore()
+      browser.close()
+    })
+
     it('should show the error on all pages', async () => {
       const aboutPage = new File(join(__dirname, '../', 'pages', 'hmr', 'about.js'))
       aboutPage.replace('</div>', 'div')