Enable context isolation on child windows

spec/api-browser-window-spec.js

@@ -1903,6 +1903,15 @@ describe('BrowserWindow module', function () {
       })
       w.loadURL('file://' + fixtures + '/api/isolated.html')
     })
+
+    it('enables context isolation on child windows', function (done) {
+      app.once('browser-window-created', function (event, window) {
+        assert.equal(window.webContents.getWebPreferences().contextIsolation, true)
+        done()
+      })
+
+      w.loadURL('file://' + fixtures + '/pages/window-open.html')
+    })
   })
 
   describe('offscreen rendering', function () {