Add @@species/better subclassing support to Promises

test/mjsunit/harmony/promise-species.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-species --allow-natives-syntax
+
+// Test that Promises use @@species appropriately
+
+// Another constructor with no species will not be instantiated
+var test = new Promise(function(){});
+var bogoCount = 0;
+function bogusConstructor() { bogoCount++; }
+test.constructor = bogusConstructor;
+assertTrue(Promise.resolve(test) instanceof Promise);
+assertFalse(Promise.resolve(test) instanceof bogusConstructor);
+// Tests that chromium:575314 is fixed thoroughly
+Promise.resolve(test).catch(e => %AbortJS("Error " + e)).then(() => {
+  if (bogoCount != 0) %AbortJS("bogoCount was " + bogoCount + " should be 0");
+});
+
+// If there is a species, it will be instantiated
+// @@species will be read exactly once, and the constructor is called with a
+// function
+var count = 0;
+var params;
+class MyPromise extends Promise {
+  constructor(...args) {
+    super(...args);
+    params = args;
+  }
+  static get [Symbol.species]() {
+    count++
+    return this;
+  }
+}
+
+var myPromise = MyPromise.resolve().then();
+assertEquals(1, count);
+assertEquals(1, params.length);
+assertEquals('function', typeof(params[0]));
+assertTrue(myPromise instanceof MyPromise);
+assertTrue(myPromise instanceof Promise);