diff -r 000000000000 -r 6474c204b198 b2g/components/test/mochitest/filepicker_path_handler_chrome.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/b2g/components/test/mochitest/filepicker_path_handler_chrome.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,31 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+* License, v. 2.0. If a copy of the MPL was not distributed with this file,
+* You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+'use strict';
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+
+// use ppmm to handle file-picker message.
+let ppmm = Cc['@mozilla.org/parentprocessmessagemanager;1']
+             .getService(Ci.nsIMessageListenerManager);
+
+let pickResult = null;
+
+function processPickMessage(message) {
+  let sender = message.target.QueryInterface(Ci.nsIMessageSender);
+  // reply FilePicker's message
+  sender.sendAsyncMessage('file-picked', pickResult);
+  // notify caller
+  sendAsyncMessage('file-picked-posted', { type: 'file-picked-posted' });
+}
+
+function updatePickResult(result) {
+  pickResult = result;
+  sendAsyncMessage('pick-result-updated', { type: 'pick-result-updated' });
+}
+
+ppmm.addMessageListener('file-picker', processPickMessage);
+// use update-pick-result to change the expected pick result.
+addMessageListener('update-pick-result', updatePickResult);