Add onChange event to preference extension APIs.

chrome/browser/extensions/extension_content_settings_apitest.cc

 // 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.
 
 #include "chrome/browser/extensions/extension_apitest.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/pref_names.h"
@@ skipping 56 matching lines @@
   pref_service->SetBoolean(prefs::kBlockThirdPartyCookies, true);
 
   EXPECT_TRUE(RunExtensionTest("content_settings/clear")) << message_;
 
   const PrefService::Preference* pref = pref_service->FindPreference(
       prefs::kBlockThirdPartyCookies);
   ASSERT_TRUE(pref);
   EXPECT_FALSE(pref->IsExtensionControlled());
   EXPECT_EQ(true, pref_service->GetBoolean(prefs::kBlockThirdPartyCookies));
 }
+
+IN_PROC_BROWSER_TEST_F(ExtensionApiTest, ContentSettingsOnChange) {
+  CommandLine::ForCurrentProcess()->AppendSwitch(
+      switches::kEnableExperimentalExtensionApis);
+
+  PrefService* prefs = browser()->profile()->GetPrefs();
+  prefs->SetBoolean(prefs::kBlockThirdPartyCookies, false);
+
+  EXPECT_TRUE(RunExtensionTestIncognito("content_settings/onchange")) <<
+      message_;
+}