Add test case for RO-space string used as property key.

R=delphick@chromium.org, jgruber@chromium.org

Bug: chromium:911416
Change-Id: Ib23ba11f3219fde183b4b9b352b13564b6e9e1e2
Reviewed-on: https://chromium-review.googlesource.com/c/1362952Reviewed-by: Dan Elphick <delphick@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58117}

test/mjsunit/regress/regress-crbug-911416.js

+// Copyright 2018 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.
+
+assertEquals(7, ({[Symbol.hasInstance.description]:7})["Symbol.hasInstance"]);