Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/notifications/notification_ui_manager_impl.cc

 // 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.
 
 #include "chrome/browser/notifications/notification_ui_manager_impl.h"
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/stl_util.h"
 #include "chrome/browser/browser_process.h"
@@ skipping 215 matching lines @@
     notifications->push_back(&(*queued_iter)->notification());
   }
 }
 
 void NotificationUIManagerImpl::Observe(
     int type,
     const content::NotificationSource& source,
     const content::NotificationDetails& details) {
   if (type == chrome::NOTIFICATION_APP_TERMINATING) {
     CancelAll();
-  } else if (type == chrome::NOTIFICATION_PREF_CHANGED) {
-    std::string* name = content::Details<std::string>(details).ptr();
-    if (*name == prefs::kDesktopNotificationPosition)
-      balloon_collection_->SetPositionPreference(
-          static_cast<BalloonCollection::PositionPreference>(
-              position_pref_.GetValue()));
   } else {
     NOTREACHED();
   }
 }
+
+void NotificationUIManagerImpl::OnPreferenceChanged(
+    PrefServiceBase* service,
+    const std::string& pref_name) {
+  if (pref_name == prefs::kDesktopNotificationPosition) {
+    balloon_collection_->SetPositionPreference(
+        static_cast<BalloonCollection::PositionPreference>(
+            position_pref_.GetValue()));
+  }
+}