Assert built-in prototype isolation

spec/fixtures/api/isolated-preload.js

@@ -8,7 +8,9 @@ window.addEventListener('message', (event) => {
       preloadProperty: typeof window.foo,
       pageProperty: typeof window.hello,
       typeofRequire: typeof require,
-      typeofProcess: typeof process
+      typeofProcess: typeof process,
+      typeofArrayPush: typeof Array.prototype.push,
+      typeofFunctionApply: typeof Function.prototype.apply
     },
     pageContext: event.data
   })

spec/fixtures/api/isolated.html

@@ -5,11 +5,15 @@
     <title>Isolated World</title>
     <script>
       window.hello = 'world'
+      Array.prototype.push = 3
+      Function.prototype.apply = true
       window.postMessage({
         preloadProperty: typeof window.foo,
         pageProperty: typeof window.hello,
         typeofRequire: typeof require,
-        typeofProcess: typeof process
+        typeofProcess: typeof process,
+        typeofArrayPush: typeof Array.prototype.push,
+        typeofFunctionApply: typeof Function.prototype.apply
       }, '*')
     </script>
   </head>