[Proxies] Support constructable proxy as new.target (reland)

test/mjsunit/es6/classes-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.
+
+// Flags: --allow-natives-syntax --harmony-proxies --harmony-reflect
+
+function CreateConstructableProxy(handler) {
+  return Proxy.createFunction(handler, function() {}, function() {});
+}
+
+(function() {
+  var prototype = { x: 1 };
+  var log = [];
+
+  var proxy = CreateConstructableProxy({
+    get(k) {
+      log.push("get trap");
+      return prototype;
+    }});
+
+  var o = Reflect.construct(Number, [100], proxy);
+  assertEquals(["get trap"], log);
+  assertTrue(Object.getPrototypeOf(o) === prototype);
+  assertEquals(100, Number.prototype.valueOf.call(o));
+})();
+
+(function() {
+  var prototype = { x: 1 };
+  var log = [];
+
+  var proxy = CreateConstructableProxy({
+    get(k) {
+      log.push("get trap");
+      return 10;
+    }});
+
+  var o = Reflect.construct(Number, [100], proxy);
+  assertEquals(["get trap"], log);
+  assertTrue(Object.getPrototypeOf(o) === Object.prototype);
+  assertEquals(100, Number.prototype.valueOf.call(o));
+})();