Add systemInfo.cpu.onUpdated event implementation.

chrome/test/data/extensions/api_test/systeminfo/cpu/test_cpuinfo_api.js

-// Copyright (c) 2012 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.
-
-// systeminfo.cpu api test
-// browser_tests.exe --gtest_filter=SystemInfoCpuApiTest.*
-
-chrome.systemInfo = chrome.experimental.systemInfo;
-
-chrome.test.runTests([
-  function testGet() {
-    for(var i = 0; i < 20; ++i) {
-      chrome.systemInfo.cpu.get(chrome.test.callbackPass(function(result) {
-        chrome.test.assertEq(4, result.numOfProcessors);
-        chrome.test.assertEq("x86", result.archName);
-        chrome.test.assertEq("unknown", result.modelName);
-      }));
-    }
-  },
-]);
-