Add failing spec for deleted guestinstance when moving webview

spec/webview-spec.js

@@ -1254,9 +1254,27 @@ describe('<webview> tag', function () {
       document.body.appendChild(webview)
     })
 
+    it('does not delete the guestinstance attribute when moving the webview to another parent node', function (done) {
+      webview.addEventListener('dom-ready', function domReadyListener () {
+        webview.addEventListener('did-attach', function () {
+          assert(webview.guestinstance != null)
+          assert(webview.getWebContents() != null)
+          done()
+        })
+
+        document.body.replaceChild(webview, div)
+      })
+      webview.src = 'file://' + fixtures + '/pages/a.html'
+
+      const div = document.createElement('div')
+      div.appendChild(webview)
+      document.body.appendChild(div)
+    })
+
     it('does not destroy the webContents when hiding/showing the webview (regression)', function (done) {
       webview.addEventListener('dom-ready', function domReadyListener () {
         const instance = webview.getAttribute('guestinstance')
+        assert(instance != null)
 
         // Wait for event directly since attach happens asynchronously over IPC
         ipcMain.once('ELECTRON_GUEST_VIEW_MANAGER_ATTACH_GUEST', function () {