[wasm] The exports property of a wasm instance should always exist

test/mjsunit/regress/wasm/regression-663994.js

Index: test/mjsunit/regress/wasm/regression-663994.js
diff --git a/test/mjsunit/regress/wasm/regression-663994.js b/test/mjsunit/regress/wasm/regression-663994.js
new file mode 100644
index 0000000000000000000000000000000000000000..da3d7c7771d37e0bb97f5140cd94aa3d3eff0891
--- /dev/null
+++ b/test/mjsunit/regress/wasm/regression-663994.js
@@ -0,0 +1,14 @@
+// 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.
+
+// Flags: --expose-wasm
+
+load("test/mjsunit/wasm/wasm-constants.js");
+load("test/mjsunit/wasm/wasm-module-builder.js");
+
+(function() {
+  var builder = new WasmModuleBuilder();
+  var module = builder.instantiate();
+  assertTrue(typeof(module.exports) != "undefined");
+})();