Fix issue with setting __proto__ on a value

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 1376 matching lines @@
 // ECMA-262, Edition 6, section B.2.2.1.1
 function ObjectGetProto() {
   return %GetPrototype(ToObject(this));
 }
 
 
 // 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)) {
+  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 {
@@ skipping 505 matching lines @@
     for (var i = 0; i < microtasks.length; i++) {
       microtasks[i]();
     }
   }
 }
 
 function EnqueueExternalMicrotask(fn) {
   GetMicrotaskQueue().push(fn);
   %SetMicrotaskPending(true);
 }