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

R=clemensh@chromium.org
BUG=chromium:663994

Review-Url: https://codereview.chromium.org/2622563002
Cr-Commit-Position: refs/heads/master@{#42163}

src/wasm/wasm-module.cc

@@ -1764,7 +1764,7 @@ class WasmInstanceBuilder {
     }
 
     Handle<JSObject> exports_object = instance;
-    if (module_->export_table.size() > 0 && module_->origin == kWasmOrigin) {
+    if (module_->origin == kWasmOrigin) {
       // Create the "exports" object.
       Handle<JSFunction> object_function = Handle<JSFunction>(
           isolate_->native_context()->object_function(), isolate_);

test/mjsunit/regress/wasm/regression-663994.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.
+
+// 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");
+})();