Fix bug with illegal spread as single arrow parameter

test/mjsunit/harmony/regress/regress-crbug-621496.js

Index: test/mjsunit/harmony/regress/regress-crbug-621496.js
diff --git a/test/mjsunit/harmony/regress/regress-crbug-621496.js b/test/mjsunit/harmony/regress/regress-crbug-621496.js
new file mode 100644
index 0000000000000000000000000000000000000000..4db7a950394742d6ecc50050b3a87a0f04e063c0
--- /dev/null
+++ b/test/mjsunit/harmony/regress/regress-crbug-621496.js
@@ -0,0 +1,7 @@
+// 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.
+
+(function testIllegalSpreadAsSingleArrowParameter() {
+  assertThrows("(...[42]) => 42)", SyntaxError)  // will core dump, if not fixed
+})();