[proxies] Implement Proxy.revocable.

test/mjsunit/harmony/proxies-revocable.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 --harmony-reflect
+
+
+traps = [
+    "getPrototypeOf", "setPrototypeOf", "isExtensible", "preventExtensions",
+    "getOwnPropertyDescriptor", "has", "get", "set", "deleteProperty",
+    "defineProperty", "ownKeys", "apply", "construct"
+];
+// TODO(neis): Fix enumerate.
+
+var {proxy, revoke} = Proxy.revocable({}, {});
+assertEquals(0, revoke.length);
+
+assertEquals(undefined, revoke());
+for (var trap of traps) {
+  assertThrows(() => Reflect[trap](proxy), TypeError);
+}
+
+assertEquals(undefined, revoke());
+for (var trap of traps) {
+  assertThrows(() => Reflect[trap](proxy), TypeError);
+}