Using the new webkit CSS change notification instead of a mutation observer.

chrome/test/data/extensions/api_test/declarative_content/overview/background.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.
 
 var declarative = chrome.declarative;
 
 var PageStateMatcher = chrome.declarativeContent.PageStateMatcher;
 var ShowPageAction = chrome.declarativeContent.ShowPageAction;
 
 var rule0 = {
   conditions: [new PageStateMatcher({pageUrl: {hostPrefix: "test1"}}),
-               new PageStateMatcher({css: ["input[type='password']"]})],
+               // TODO(jyasskin): Normalize the CSS selector value and switch
+               // this back to single quotes.
+               new PageStateMatcher({css: ["input[type=\"password\"]"]})],
   actions: [new ShowPageAction()]
 }
 
 var testEvent = chrome.declarativeContent.onPageChanged;
 
 testEvent.removeRules(undefined, function() {
   testEvent.addRules([rule0], function() {
     chrome.test.sendMessage("ready", function(reply) {
     })
   });
 });