[proxies] Implement [[Enumerate]] and [[OwnPropertyKeys]]

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();
+  }
+}
+
+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"]);
+
+// 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);