WIP [esnext] implement async iteration proposal

test/test262/local-tests/test/language/expressions/async-generators/early-errors-expression-not-simple-assignment-target.js

Index: test/test262/local-tests/test/language/expressions/async-generators/early-errors-expression-not-simple-assignment-target.js
diff --git a/test/test262/local-tests/test/language/expressions/async-generators/early-errors-expression-not-simple-assignment-target.js b/test/test262/local-tests/test/language/expressions/async-generators/early-errors-expression-not-simple-assignment-target.js
new file mode 100644
index 0000000000000000000000000000000000000000..900b8277e1c90ec5891d86fcf087cb3c493ee633
--- /dev/null
+++ b/test/test262/local-tests/test/language/expressions/async-generators/early-errors-expression-not-simple-assignment-target.js
@@ -0,0 +1,14 @@
+// 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: pending
+description: >
+  Async generator function expressions are not a simple assignment target.
+negative:
+  phase: early
+  type: ReferenceError
+---*/
+
+(async function*() { } = 1);