Add tests for [[SetPrototypeOf]] on Object.prototype

Object.prototype is the immutable prototype exotic object

Ref tc39/ecma262#308

test/built-ins/Object/prototype/setPrototypeOf-with-different-values.js

@@ -0,0 +1,47 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+id: sec-immutable-prototype-exotic-objects-setprototypeof-v
+description: >
+  Object.prototype's [[SetPrototypeOf]] returns false if value is not the same
+info: >
+  9.4.7.1 [[SetPrototypeOf]] (V)
+
+  ...
+  2. Let current be the value of the [[Prototype]] internal slot of O.
+  3. If SameValue(V, current), return true.
+  4. Return false.
+features: [Reflect.setPrototypeOf]
+---*/
+
+var ObjProto = Object.prototype;
+
+assert.throws(TypeError, function() {
+  Object.setPrototypeOf(ObjProto, {});
+}, "Object.setPrototypeOf(ObjProto, {}) throws a TypeError");
+
+assert.throws(TypeError, function() {
+  Object.setPrototypeOf(ObjProto, Array.prototype);
+}, "Object.setPrototypeOf(ObjProto, Array.prototype) throws a TypeError");
+
+assert.throws(TypeError, function() {
+  Object.setPrototypeOf(ObjProto, null);
+}, "Object.setPrototypeOf(ObjProto, null) throws a TypeError");
+
+assert.sameValue(
+  Reflect.setPrototypeOf(ObjProto, {}),
+  false,
+  "Reflect.setPrototypeOf(ObjProto, {}) returns false"
+);
+
+assert.sameValue(
+  Reflect.setPrototypeOf(ObjProto, Array.prototype),
+  false,
+  "Reflect.setPrototypeOf(ObjProto, Array.prototype) returns false"
+);
+
+assert.sameValue(
+  Reflect.setPrototypeOf(ObjProto, null),
+  false,
+  "Reflect.setPrototypeOf(ObjProto, null) returns false"
+);

test/built-ins/Object/prototype/setPrototypeOf-with-same-value.js

@@ -0,0 +1,39 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+id: sec-immutable-prototype-exotic-objects-setprototypeof-v
+description: >
+  Object.prototype's [[SetPrototypeOf]] returns true if value is same
+info: >
+  9.4.7.1 [[SetPrototypeOf]] (V)
+
+  ...
+  2. Let current be the value of the [[Prototype]] internal slot of O.
+  3. If SameValue(V, current), return true.
+  4. Return false.
+features: [Reflect.setPrototypeOf]
+---*/
+
+var ObjProto = Object.prototype;
+
+assert.sameValue(
+  Object.setPrototypeOf(ObjProto, ObjProto),
+  ObjProto,
+  "Object.setPrototypeOf(ObjProto, ObjProto) returns the Object.prototype"
+);
+
+assert(
+  Object.isExtensible(ObjProto),
+  "Object.prototype is still extensible after a setPrototypeOf operation - #1"
+);
+
+assert.sameValue(
+  Reflect.setPrototypeOf(ObjProto, ObjProto),
+  true,
+  "Reflect.setPrototypeOf(ObjProto, ObjProto) returns true"
+);
+
+assert(
+  Object.isExtensible(ObjProto),
+  "Object.prototype is still extensible after a setPrototypeOf operation - #2"
+);