[modules] Add a simple micro-benchmark for import/export accesses.

test/js-perf-test/Modules/basic-namespace.js

Index: test/js-perf-test/Modules/basic-namespace.js
diff --git a/test/js-perf-test/Modules/basic-namespace.js b/test/js-perf-test/Modules/basic-namespace.js
new file mode 100644
index 0000000000000000000000000000000000000000..4fcdcb5fd9313f2a58a1d7d12ce3323014bd14ab
--- /dev/null
+++ b/test/js-perf-test/Modules/basic-namespace.js
@@ -0,0 +1,8 @@
+// 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.
+
+import * as m from "value.js";
+for (let i = 0; i < iterations; ++i) m.set(m.value + 1);
+if (m.value != iterations) throw m.value;
+m.set(0);