WIP [esnext] implement async iteration proposal

test/test262/local-tests/test/language/expressions/async-generators/expression-yield-as-operand.js

Index: test/test262/local-tests/test/language/expressions/async-generators/expression-yield-as-operand.js
diff --git a/test/test262/local-tests/test/language/expressions/async-generators/expression-yield-as-operand.js b/test/test262/local-tests/test/language/expressions/async-generators/expression-yield-as-operand.js
new file mode 100644
index 0000000000000000000000000000000000000000..c2a14ffcd382d7f4846994d48b9d470e53a4c3c2
--- /dev/null
+++ b/test/test262/local-tests/test/language/expressions/async-generators/expression-yield-as-operand.js
@@ -0,0 +1,31 @@
+// Copyright 2017 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+author: Caitlin Potter <caitp@igalia.com>
+esid: 14.4
+description: >
+  `yield` expressions may be used as the right-hand-side of other `yield`
+  expressions.
+flags: [async]
+---*/
+
+var g = async function*() {
+  yield yield 1;
+};
+
+var iter = g();
+iter.next().then(function(result) {
+  assert.sameValue(result.value, 1, 'First result `value`');
+  assert.sameValue(result.done, false, 'First result `done` flag');
+}).then(undefined, $DONE);
+
+iter.next().then(function(result) {
+  assert.sameValue(result.value, undefined, 'Second result `value`');
+  assert.sameValue(result.done, false, 'Second result `done` flag');
+}).then(undefined, $DONE);
+
+iter.next().then(function(result) {
+  assert.sameValue(result.value, undefined, 'Third result `value`');
+  assert.sameValue(result.done, true, 'Thid result `done` flag');
+}).then($DONE, $DONE);