Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/notifications/notification_ui_manager_impl.cc

Index: chrome/browser/notifications/notification_ui_manager_impl.cc
diff --git a/chrome/browser/notifications/notification_ui_manager_impl.cc b/chrome/browser/notifications/notification_ui_manager_impl.cc
index f02b0f5d894da6e8279157224057bf4a6f600972..bf096c3d0190d63c9cb535dca0adaf52af5c9d52 100644
--- a/chrome/browser/notifications/notification_ui_manager_impl.cc
+++ b/chrome/browser/notifications/notification_ui_manager_impl.cc
@@ -233,13 +233,17 @@ void NotificationUIManagerImpl::Observe(
     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()));
+  }
+}