ES6: Tighten up Object.prototype.__proto__

src/v8natives.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1366 matching lines @@
 // Harmony egal.
 function ObjectIs(obj1, obj2) {
   if (obj1 === obj2) {
     return (obj1 !== 0) || (1 / obj1 === 1 / obj2);
   } else {
     return (obj1 !== obj1) && (obj2 !== obj2);
   }
 }
 
 
-// Harmony __proto__ getter.
+// ECMA-262, Edition 6, section B.2.2.1.1
 function ObjectGetProto() {
-  return %GetPrototype(this);
+  return %GetPrototype(ToObject(this));
 }
 
 
-// Harmony __proto__ setter.
-function ObjectSetProto(obj) {
-  return %SetPrototype(this, obj);
+// ECMA-262, Edition 6, section B.2.2.1.2
+function ObjectSetProto(proto) {
+  CHECK_OBJECT_COERCIBLE(this, "Object.prototype.__proto__");
+
+  if (IS_SPEC_OBJECT(proto) || IS_NULL(proto) && IS_SPEC_OBJECT(this)) {
+    %SetPrototype(this, proto);
+  }
 }
 
 
 function ObjectConstructor(x) {
   if (%_IsConstructCall()) {
     if (x == null) return this;
     return ToObject(x);
   } else {
     if (x == null) return { };
     return ToObject(x);
@@ skipping 488 matching lines @@
 function RunMicrotasks() {
   while (%SetMicrotaskPending(false)) {
     var microtasks = RunMicrotasks.queue;
     RunMicrotasks.queue = new InternalArray;
 
     for (var i = 0; i < microtasks.length; i++) {
       microtasks[i]();
     }
   }
 }