[async-iteration] expose Symbol.asyncIterator behind flag --harmony-async-iteration

test/mjsunit/harmony/symbol-async-iterator.js

+// Copyright 2017 the V8 project authors. All rights reserved.

[Dan Ehrenberg, 2017/01/19 21:55:25]

Would it work to write this as a test262 test instad?

[caitp, 2017/01/19 21:58:38]

I mentioned this offline, but:

I believe this test has already been written by one of those other contributors,
but is not upstream yet, and I have no idea when it will be upstream. So in the
interest of not waiting for them, there's a simple test here.

We can get rid of it after a test262 roll that includes a duplicate test

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-async-iteration
+
+assertTrue(Symbol.hasOwnProperty("asyncIterator"));
+assertEquals("symbol", typeof Symbol.asyncIterator);
+assertInstanceof(Object(Symbol.asyncIterator), Symbol);
+
+let desc = Object.getOwnPropertyDescriptor(Symbol, "asyncIterator");
+assertFalse(desc.writable);
+assertFalse(desc.enumerable);
+assertFalse(desc.configurable);