Add a --harmony-species flag, defining @@species on constructors

test/mjsunit/harmony/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
+
+// Test the ES2015 @@species feature
+
+'use strict';
+
+let TypedArray = Uint8Array.__proto__;
+
+// The @@species property exists on the right objects and has the right values
+
+let classesWithSpecies = [RegExp, Array, TypedArray, ArrayBuffer, Map, Set, Promise];
+let classesWithoutSpecies = [Object, Function, String, Number, Symbol, WeakMap, WeakSet];
+
+for (let constructor of classesWithSpecies) {
+  assertEquals(constructor, constructor[Symbol.species]);
+  assertThrows(function() { constructor[Symbol.species] = undefined }, TypeError);
+  let descriptor = Object.getOwnPropertyDescriptor(constructor, Symbol.species);
+  assertTrue(descriptor.configurable);
+  assertFalse(descriptor.enumerable);
+  assertEquals(undefined, descriptor.writable);
+  assertEquals(undefined, descriptor.set);
+  assertEquals('function', typeof descriptor.get);
+}
+
+// @@species is defined with distinct getters
+assertEquals(classesWithSpecies.length,
+             new Set(classesWithSpecies.map(constructor =>
+                                            Object.getOwnPropertyDescriptor(
+                                              constructor, Symbol.species).get)
+                ).size);
+
+for (let constructor of classesWithoutSpecies)
+  assertEquals(undefined, constructor[Symbol.species]);