Support global keyboard commands on Chrome OS.

chrome/test/data/extensions/api_test/keybinding/global/background.js

 // Copyright (c) 2013 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.
 
 // Called when the user activates the command.
 chrome.commands.onCommand.addListener(function(command) {
-  if (command == "Ctrl-Shift-9-Valid-Global-Shortcut") {
+  if (command == "Ctrl-Shift-8-Valid-Global-Shortcut") {
     chrome.test.notifyPass();
     return;
   }
 
   // Everything else is a failure case.
   chrome.test.notifyFail("Unexpected command received: " + command);
 });
 
 chrome.test.notifyPass();