Add private system extension API to get system update status

chrome/test/data/extensions/api_test/system/get_update_status/background.js

+// Copyright (c) 2011 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.
+
+// systemPrivate.getUpdateStatus test for Chrome
+// browser_tests --gtest_filter="GetUpdateStatusApiTest.Progress"
+
+chrome.test.runTests([
+  function notAvailable() {
+    chrome.systemPrivate.getUpdateStatus(function(status) {
+      chrome.test.assertEq(status.state, "NotAvailable");
+      chrome.test.assertEq(status.download_progress, 0.0);
+      chrome.test.succeed();
+    });
+  },
+  function updating() {
+    chrome.systemPrivate.getUpdateStatus(function(status) {
+      chrome.test.assertEq(status.state, "Updating");
+      chrome.test.assertEq(status.download_progress, 0.5);
+      chrome.test.succeed();
+    });
+  },
+  function needRestart() {
+    chrome.systemPrivate.getUpdateStatus(function(status) {
+      chrome.test.assertEq(status.state, "NeedRestart");
+      chrome.test.assertEq(status.download_progress, 1);
+      chrome.test.succeed();
+    });
+  }
+]);