Remove content::NotificationObserver dependency from most Prefs code.

chrome/common/chrome_notification_types.h

Index: chrome/common/chrome_notification_types.h
diff --git a/chrome/common/chrome_notification_types.h b/chrome/common/chrome_notification_types.h
index 01fed074168a454d094f127c81de0f07fa13aadb..1245ae709d20efc2079b40d638be44789df0789b 100644
--- a/chrome/common/chrome_notification_types.h
+++ b/chrome/common/chrome_notification_types.h
@@ -406,14 +406,6 @@ enum NotificationType {
   // to policy.  Source and details are unused.
   NOTIFICATION_DEFAULT_SEARCH_POLICY_CHANGED,
 
-  // This is sent to a pref observer when a pref is changed. The source is the
-  // PrefService and the details a std::string of the changed path.
-  NOTIFICATION_PREF_CHANGED,
-
-  // This is broadcast after the preference subsystem has completed
-  // asynchronous initalization of a PrefService.
-  NOTIFICATION_PREF_INITIALIZATION_COMPLETED,
-
   // The state of a web resource has been changed. A resource may have been
   // added, removed, or altered. Source is WebResourceService, and the
   // details are NoDetails.