[test] Add regression test for http://crbug.com/642056.

The bug itself was already fixed in ToT as part of
http://crrev.com/2263273003.

R=machenbach@chromium.org
BUG=chromium:642056

Review-Url: https://codereview.chromium.org/2306913002
Cr-Commit-Position: refs/heads/master@{#39117}

test/mjsunit/regress/regress-crbug-642056.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: --allow-natives-syntax
+
+function f(o) {
+  return o.x instanceof Array;
+}
+
+var o = { x : 1.5 };
+o.x = 0;
+
+f(o);
+f(o);
+%OptimizeFunctionOnNextCall(f);
+f(o);