Add hook for extension to check sync status.

chrome/test/data/extensions/api_test/preferences_private/test.js

+// Copyright 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.
+
+chrome.test.runTests([function() {
+  chrome.preferencesPrivate.getSyncCategoriesWithoutPassphrase(
+    chrome.test.callbackPass(
+      function(categories) {
+        chrome.test.assertTrue(categories.indexOf("Bookmarks") >= 0,
+            "Bookmarks is missing.");
+        chrome.test.assertTrue(categories.indexOf("Preferences") >= 0,
+            "Preferences is missing.");
+        chrome.test.assertTrue(categories.indexOf("Autofill") == -1,
+            "Autofill present even though it's encrypted.");
+        chrome.test.assertTrue(categories.indexOf("Typed URLs") == -1,
+            "Typed URLs present even though it's not synced.");
+      }
+    )
+  );
+}]);