Fix broken PrefService::preference_set() returning not all registered preferences.

chrome/test/functional/PYAUTO_TESTS

 # Copyright (c) 2010 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.
 #
 # This file lists the pyauto tests that run as a part of the functional test
 # suite.
 #
 # Tests can be enabled on a per-platform basis. Tests not listed here will
 # not be run.
 #
@@ skipping 49 matching lines @@
       '-notifications.NotificationsTest.testNotificationOrderAfterClosingOne',
       '-notifications.NotificationsTest.testKillNotificationProcess',
       'ntp',
       'omnibox',
       'passwords',
       'pdf',
       'plugins',
       'popups',
       '-popups',  # Flaky. crbug.com/70659
       'prefs',
-      # Some pref tests broken by r72489. crbug.com/70809
-      '-prefs.PrefsTest.testUnderTheHoodPref',
-      '-prefs.PrefsTest.testHomepagePrefs',
       'search_engines',
       # crbug.com/67628
       '-search_engines.SearchEnginesTest.testTabToSearch',
       # crbug.com/70439
       '-search_engines.SearchEnginesTest.testAddSearchEngine',
       '-search_engines.SearchEnginesTest.testEditSearchEngine',
       '-search_engines.SearchEnginesTest.testSearchEngineSpecialChars',
       'special_tabs',
       # crbug.com/67851
       '-special_tabs.SpecialTabsTest.testAboutDNSTab',
@@ skipping 101 matching lines @@
     'linux': [
     ],
 
     'chromeos': [
       # crosbug.com/6856
       '-translate.TranslateTest.testSessionRestore',
       '-translate.TranslateTest.testDownloadsNotTranslated',
     ],
   }
 }