Suppress the exception thrown when responding to message with no response callback.

chrome/test/data/extensions/hotword/test.js

Index: chrome/test/data/extensions/hotword/test.js
diff --git a/chrome/test/data/extensions/hotword/test.js b/chrome/test/data/extensions/hotword/test.js
new file mode 100644
index 0000000000000000000000000000000000000000..51a8c808ccd7353cb4b48d633bbd07137a3561fb
--- /dev/null
+++ b/chrome/test/data/extensions/hotword/test.js
@@ -0,0 +1,17 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Send a WAKE_UP command to the hotword helper extension.
+chrome.runtime.sendMessage(
+    'dnhpdliibojhegemfjheidglijccjfmc',
+    {type: 'wu'});
+
+// Assume messages are delivered in-order. In this case, this message will be
+// handled after the previous one, and indicates the test case has completed.
+chrome.runtime.sendMessage(
+    'dnhpdliibojhegemfjheidglijccjfmc',
+    {type: 'wu'},
+    function() {
+      chrome.test.sendMessage("done");
+    });