Implement immutable prototype chains

test/mjsunit/es6/proxies-global-reference.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.
 
 var failing_proxy = new Proxy({}, new Proxy({}, {
   get() { throw "No trap should fire" }}));
 
-Object.setPrototypeOf(Object.prototype, failing_proxy);
-assertThrows(()=>a, TypeError);
-
-Object.setPrototypeOf(this, failing_proxy);
-assertThrows(()=>a, TypeError);
+assertThrows(() => Object.setPrototypeOf(Object.prototype, failing_proxy), TypeError);
+assertThrows(()=>a, ReferenceError);

[Dan Ehrenberg, 2016/06/29 18:04:01]

The loss of this test is a bit unfortunate, but it could be reconstituted with a
cctest which constructs the right sort of global object and manipulates its
proto chain. However, that test will soon be obsolete when the code path is
removed after making Blink's prototype chain immutable per spec.