[proxies] [[HasProperty]]: fix trap call.

test/mjsunit/harmony/proxies-enumerate.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_one": 1
 };
 target.__proto__ = {
   "target_two": 2
 };
 var handler = {
   enumerate: function(target) {
     function* keys() {
       yield "foo";
       yield "bar";
     }
     return keys();
+  },
+  // For-in calls "has" on every iteration, so for TestForIn() below to
+  // detect all results of the "enumerate" trap, "has" must return true.
+  has: function(target, name) {
+    return true;
   }
 }
 
 var proxy = new Proxy(target, handler);
 
 function TestForIn(receiver, expected) {
   var result = [];
   for (var k in receiver) {
     result.push(k);
   }
   assertEquals(expected, result);
 }
 
 TestForIn(proxy, ["foo", "bar"]);
 
 // Properly call traps on proxies on the prototype chain.
 var receiver = {
   "receiver_one": 1
 };
 receiver.__proto__ = proxy;
-// TODO(jkummerow): Needs proper 'has' trap; implement that and enable this!
-// TestForIn(receiver, ["receiver_one", "foo", "bar"]);
+TestForIn(receiver, ["receiver_one", "foo", "bar"]);
 
 // Fall through to default behavior when trap is undefined.
 handler.enumerate = undefined;
 TestForIn(proxy, ["target_one", "target_two"]);
 delete handler.enumerate;
 TestForIn(proxy, ["target_one", "target_two"]);
 
 // Non-string keys must be filtered.
 function TestNonStringKey(key) {
   handler.enumerate = function(target) {
     function* keys() { yield key; }
     return keys();
   }
   assertThrows("for (var k in proxy) {}", TypeError);
 }
 
 TestNonStringKey(1);
 TestNonStringKey(3.14);
 TestNonStringKey(Symbol("foo"));
 TestNonStringKey({bad: "value"});
 TestNonStringKey(null);
 TestNonStringKey(undefined);
 TestNonStringKey(true);