[bootstrapper] extra natives must not use natives syntax.

test/cctest/test-extra.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function (global, binding, v8) {
   'use strict';
   binding.testExtraShouldReturnFive = function() {
     return 5;
   };
 
   binding.testExtraShouldCallToRuntime = function() {
     return binding.runtime(3);
   };
 
+  binding.testFunctionToString = function() {
+    function foo() { return 1; }
+    return foo.toString();
+  };
+
+  binding.testStackTrace = function(f) {
+    return f();
+  }
+
   // Exercise all of the extras utils:
   // - v8.createPrivateSymbol
   // - v8.simpleBind, v8.uncurryThis
   // - v8.InternalPackedArray
   // - v8.createPromise, v8.resolvePromise, v8.rejectPromise
 
   const Object = global.Object;
   const hasOwn = v8.uncurryThis(Object.prototype.hasOwnProperty);
 
   const Function = global.Function;
@@ skipping 32 matching lines @@
     }, null, new v8.InternalPackedArray('x', 'x')));
 
     return {
       privateSymbol: v8.createPrivateSymbol('sym'),
       fulfilledPromise, // should be fulfilled with 1
       fulfilledPromise2, // should be fulfilled with 2
       rejectedPromise // should be rejected with 3
     };
   };
 })