Add test case for Number.prototype.toString (r42364).

TBR=tebbi@chromium.org
BUG=chromium:679841

Review-Url: https://codereview.chromium.org/2631163002
Cr-Commit-Position: refs/heads/master@{#42375}

test/mjsunit/regress/regress-crbug-679841.js

+// Copyright 2017 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.
+
+(-1e-301).toString(2);