Add test case for 85b8c2dc (fix observable array access in messages.js).

R=bmeurer@chromium.org
BUG=chromium:617527

Review-Url: https://codereview.chromium.org/2045153002
Cr-Commit-Position: refs/heads/master@{#36813}

test/mjsunit/regress/regress-crbug-617527.js

+// Copyright 2016 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: --enable-slow-asserts
+
+Object.defineProperty(Array.prototype, "1", { get: toLocaleString });
+assertThrows(_ => new RegExp(0, 0));