[runtime] [proxy] Adding [[SetPrototypeOf]] trap.

test/mjsunit/harmony/proxies-set-prototype-of.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.
+
+// Flags: --harmony-proxies
+
+var target = { target: 1 };
+target.__proto__ = {};
+var handler = { handler: 1 };
+var proxy = new Proxy(target, handler);
+
+assertSame(Object.getPrototypeOf(proxy), target.__proto__ );
+
+assertThrows(function() { Object.setPrototypeOf(proxy, undefined) }, TypeError);
+assertThrows(function() { Object.setPrototypeOf(proxy, 1) }, TypeError);
+
+var prototype = [1];
+assertSame(proxy, Object.setPrototypeOf(proxy, prototype));
+assertSame(prototype, Object.getPrototypeOf(proxy));
+assertSame(prototype, Object.getPrototypeOf(target));
+
+handler.setPrototypeOf = function(target, proto) {
+  return false;
+};
+assertThrows(function() { Object.setPrototypeOf(proxy, {a:1}) }, TypeError);
+
+handler.setPrototypeOf = function(target, proto) {
+  return undefined;
+};
+assertThrows(function() { Object.setPrototypeOf(proxy, {a:2}) }, TypeError);
+
+handler.setPrototypeOf = function(proto) {};
+assertThrows(function() { Object.setPrototypeOf(proxy, {a:3}) }, TypeError);
+
+handler.setPrototypeOf = function(target, proto) {
+  throw Error();
+};
+assertThrows(function() { Object.setPrototypeOf(proxy, {a:4}) }, Error);
+
+var seen_prototype;
+var seen_target;
+handler.setPrototypeOf = function(target, proto) {
+  seen_target = target;
+  seen_prototype = proto;
+  return true;
+}
+assertSame(Object.setPrototypeOf(proxy, {a:5}), proxy);
+assertSame(target, seen_target);
+assertEquals({a:5}, seen_prototype);
+
+// Target is a Proxy:
+var target2 = new Proxy(target, {});
+var proxy2 = new Proxy(target2, {});
+assertSame(Object.getPrototypeOf(proxy2), target.__proto__ );
+
+prototype = [2,3];
+assertSame(proxy2, Object.setPrototypeOf(proxy2, prototype));
+assertSame(prototype, Object.getPrototypeOf(proxy2));
+assertSame(prototype, Object.getPrototypeOf(target));