Missing runtime test

TBR=svenpanne@chromium.org
BUG=

Review URL: https://codereview.chromium.org/407943002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22503 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

test/mjsunit/runtime-gen/functionisarrow.js

+// Copyright 2014 the V8 project authors. All rights reserved.
+// AUTO-GENERATED BY tools/generate-runtime-tests.py, DO NOT MODIFY
+// Flags: --allow-natives-syntax --harmony
+var arg0 = () => null;
+%FunctionIsArrow(arg0);