fix contextIsolation issue while webPreference sandbox is on

contextIsolation didn't work while sandbox is on. The fix is contextIsolation picked up while sandbox on

spec/fixtures/api/isolated-preload.js

@@ -1,14 +1,11 @@
 // Ensure fetch works from isolated world origin
 fetch('http://localhost:1234')
 fetch('https://localhost:1234')
-fetch(`file://${__filename}`)
 
 const {ipcRenderer, webFrame} = require('electron')
 
 window.foo = 3
 
-webFrame.executeJavaScript('window.preloadExecuteJavaScriptProperty = 1234;')
-
 window.addEventListener('message', (event) => {
   ipcRenderer.send('isolated-world', {
     preloadContext: {
@@ -21,4 +18,15 @@ window.addEventListener('message', (event) => {
     },
     pageContext: event.data
   })
+  ipcRenderer.send('isolated-sandbox-world', {
+    preloadContext: {
+      preloadProperty: typeof window.foo,
+      pageProperty: typeof window.hello,
+      typeofRequire: typeof require,
+      typeofProcess: typeof process,
+      typeofArrayPush: typeof Array.prototype.push,
+      typeofFunctionApply: typeof Function.prototype.apply
+    },
+    pageContext: event.data
+  })
 })