Add test for Promises subclassing.

test/mjsunit/es6/classes-subclass-builtins.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-reflect --harmony-regexp-subclass
 // Flags: --expose-gc
 
 "use strict";
 
 
@@ skipping 529 matching lines @@
   assertPropertiesEqual({done: true, value: undefined}, o.next());
 
   var generator_func1 = new A("return 0;");
   assertTrue(%HaveSameMap(generator_func, generator_func1));
 
   gc();
 })();
 
 
 (function() {
+  class A extends Promise {
+    constructor(...args) {
+      assertTrue(%IsConstructCall());
+      super(...args);
+      this.a = 42;
+      this.d = 4.2;
+      this.o = {foo:153};
+    }
+  }
+
+  var o = new A(function(resolve, reject) {
+    resolve("ok");
+  });
+  assertTrue(o instanceof Object);
+  assertTrue(o instanceof Promise);
+  assertTrue(o instanceof A);
+  assertEquals("object", typeof o);
+  checkPrototypeChain(o, [A, Promise, Object]);
+  assertEquals(42, o.a);
+  assertEquals(4.2, o.d);
+  assertEquals(153, o.o.foo);
+  o.then(
+      function(val) { assertEquals("ok", val); },
+      function(reason) { assertUnreachable(); })
+    .catch(function(reason) { %AbortJS("catch handler called: " + reason); });
+
+  var o1 = new A(function(resolve, reject) {
+    reject("fail");
+  });
+  o1.then(
+      function(val) { assertUnreachable(); },
+      function(reason) { assertEquals("fail", reason); })
+    .catch(function(reason) { %AbortJS("catch handler called: " + reason); });
+  assertTrue(%HaveSameMap(o, o1));
+
+  gc();
+})();
+
+
+(function() {
   class A extends Boolean {
     constructor() {
       assertTrue(%IsConstructCall());
       super(true);
       this.a00 = 0
       this.a01 = 0
       this.a02 = 0
       this.a03 = 0
       this.a04 = 0
       this.a05 = 0
@@ skipping 221 matching lines @@
 
   Object.defineProperty(pattern, Symbol.match, {
     get() { log.push("match"); f.prototype = p2; return false; }});
 
   var o = Reflect.construct(RegExp, [pattern], f);
   assertEquals(["match", "tostring"], log);
   assertEquals(/biep/, o);
   assertTrue(o.__proto__ === p2);
   assertTrue(f.prototype === p3);
 })();