Implement immutable prototype chains

test/mjsunit/es6/proxies-global-reference.js

Index: test/mjsunit/es6/proxies-global-reference.js
diff --git a/test/mjsunit/es6/proxies-global-reference.js b/test/mjsunit/es6/proxies-global-reference.js
index 975d7f75fb27a87a719277ba386d192a103bfa36..1e3d3beb8658bb1e9d009f20a1919dd7dc958e79 100644
--- a/test/mjsunit/es6/proxies-global-reference.js
+++ b/test/mjsunit/es6/proxies-global-reference.js
@@ -5,8 +5,5 @@
 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);