Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/translate/translate_manager.cc

Index: chrome/browser/translate/translate_manager.cc
diff --git a/chrome/browser/translate/translate_manager.cc b/chrome/browser/translate/translate_manager.cc
index b3bdca7e9620690d691bf921cea4113b622e4c92..b423325c3873352e94eafc9767a0dcbfe492c8bd 100644
--- a/chrome/browser/translate/translate_manager.cc
+++ b/chrome/browser/translate/translate_manager.cc
@@ -409,18 +409,17 @@ void TranslateManager::Observe(int type,
       delete pref_change_registrar;
       break;
     }
-    case chrome::NOTIFICATION_PREF_CHANGED: {
-      DCHECK(*content::Details<std::string>(details).ptr() ==
-             prefs::kAcceptLanguages);
-      PrefService* prefs = content::Source<PrefService>(source).ptr();
-      InitAcceptLanguages(prefs);
-      break;
-    }
     default:
       NOTREACHED();
   }
 }
 
+void TranslateManager::OnPreferenceChanged(PrefServiceBase* service,
+                                           const std::string& pref_name) {
+  DCHECK_EQ(prefs::kAcceptLanguages, pref_name);
+  InitAcceptLanguages(static_cast<PrefService*>(service));
+}
+
 void TranslateManager::OnURLFetchComplete(const net::URLFetcher* source) {
   if (translate_script_request_pending_.get() != source &&
       language_list_request_pending_.get() != source) {