[proxies] Implement Proxy.revocable.

src/js/proxy.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.
 
 (function(global, utils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 24 matching lines @@
     constructTrap = function() {
       return %Apply(construct, UNDEFINED, arguments, 0, %_ArgumentsLength());
     }
   } else {
     throw MakeTypeError(kProxyTrapFunctionExpected, "construct")
   }
   return %CreateJSFunctionProxy(
     {}, handler, callTrap, constructTrap, GlobalFunction.prototype)
 }
 
+function ProxyCreateRevocable(target, handler) {
+  var p = new GlobalProxy(target, handler);
+  return {proxy: p, revoke: () => %RevokeProxy(p)};
+}
+
 // -------------------------------------------------------------------
 // Proxy Builtins
 
 function DerivedConstructTrap(callTrap) {
   return function() {
     var proto = this.prototype
     if (!IS_SPEC_OBJECT(proto)) proto = GlobalObject.prototype
     var obj = { __proto__: proto };
     var result = %Apply(callTrap, obj, arguments, 0, %_ArgumentsLength());
     return IS_SPEC_OBJECT(result) ? result : obj
@@ skipping 82 matching lines @@
     }
     result.push(key);
   }
   return result;
 }
 
 //-------------------------------------------------------------------
 
 //Set up non-enumerable properties of the Proxy object.
 utils.InstallFunctions(GlobalProxy, DONT_ENUM, [
+  "revocable", ProxyCreateRevocable,
   "createFunction", ProxyCreateFunction
 ]);
 
 // -------------------------------------------------------------------
 // Exports
 
 utils.Export(function(to) {
   to.ProxyDelegateCallAndConstruct = DelegateCallAndConstruct;
   to.ProxyDerivedHasOwnTrap = DerivedHasOwnTrap;
 });
 
 %InstallToContext([
   "proxy_enumerate", ProxyEnumerate,
 ]);
 
 })